[patch 00/10 -mm v3] oom killer rewrite

[patch 00/10 -mm v3] oom killer rewrite

[David Rientjes]

This patchset is a rewrite of the out of memory killer to address several
issues that have been raised recently.  The most notable change is a
complete rewrite of the badness heuristic that determines which task is
killed; the goal was to make it as simple and predictable as possible
while still addressing issues that plague the VM.

Changes from version 2:

 - updated to mmotm-2010-03-09-19-15

 - schedule a timeout for current if it was not selected for oom kill
   when it has returned VM_FAULT_OOM so memory can freed to prevent
   needlessly recalling the oom killer and looping.

To apply, download the -mm tree from
http://userweb.kernel.org/~akpm/mmotm/broken-out.tar.gz first.

This patchset is also available for each kernel release from:

	http://www.kernel.org/pub/linux/kernel/people/rientjes/oom-killer-rewrite/

including broken out patches.
---
 Documentation/feature-removal-schedule.txt |   30 +
 Documentation/filesystems/proc.txt         |  100 +++--
 Documentation/sysctl/vm.txt                |   51 +-
 fs/proc/base.c                             |  106 +++++
 include/linux/memcontrol.h                 |    8 
 include/linux/mempolicy.h                  |   13 
 include/linux/oom.h                        |   24 +
 include/linux/sched.h                      |    3 
 kernel/exit.c                              |    8 
 kernel/fork.c                              |    1 
 kernel/sysctl.c                            |   15 
 mm/memcontrol.c                            |    8 
 mm/mempolicy.c                             |   44 ++
 mm/oom_kill.c                              |  567 +++++++++++++++--------------
 mm/page_alloc.c                            |   29 +
 15 files changed, 655 insertions(+), 352 deletions(-)

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[patch 01/10 -mm v3] oom: filter tasks not sharing the same cpuset

[David Rientjes]

Tasks that do not share the same set of allowed nodes with the task that
triggered the oom should not be considered as candidates for oom kill.

Tasks in other cpusets with a disjoint set of mems would be unfairly
penalized otherwise because of oom conditions elsewhere; an extreme
example could unfairly kill all other applications on the system if a
single task in a user's cpuset sets itself to OOM_DISABLE and then uses
more memory than allowed.

Killing tasks outside of current's cpuset rarely would free memory for
current anyway.  To use a sane heuristic, we must ensure that killing a
task would likely free memory for current and avoid needlessly killing
others at all costs just because their potential memory freeing is
unknown.  It is better to kill current than another task needlessly.

Acked-by: Rik van Riel <riel@redhat.com>
Acked-by: Nick Piggin <npiggin@suse.de>
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: David Rientjes <rientjes@google.com>
---
 mm/oom_kill.c |   12 +++---------
 1 files changed, 3 insertions(+), 9 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -35,7 +35,7 @@ static DEFINE_SPINLOCK(zone_scan_lock);
 /* #define DEBUG */
 
 /*
- * Is all threads of the target process nodes overlap ours?
+ * Do all threads of the target process overlap our allowed nodes?
  */
 static int has_intersects_mems_allowed(struct task_struct *tsk)
 {
@@ -167,14 +167,6 @@ unsigned long badness(struct task_struct *p, unsigned long uptime)
 		points /= 4;
 
 	/*
-	 * If p's nodes don't overlap ours, it may still help to kill p
-	 * because p may have allocated or otherwise mapped memory on
-	 * this node before. However it will be less likely.
-	 */
-	if (!has_intersects_mems_allowed(p))
-		points /= 8;
-
-	/*
 	 * Adjust the score by oom_adj.
 	 */
 	if (oom_adj) {
@@ -266,6 +258,8 @@ static struct task_struct *select_bad_process(unsigned long *ppoints,
 			continue;
 		if (mem && !task_in_mem_cgroup(p, mem))
 			continue;
+		if (!has_intersects_mems_allowed(p))
+			continue;
 
 		/*
 		 * This task already has access to memory reserves and is

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[patch 02/10 -mm v3] oom: sacrifice child with highest badness score for parent

[David Rientjes]

When a task is chosen for oom kill, the oom killer first attempts to
sacrifice a child not sharing its parent's memory instead.
Unfortunately, this often kills in a seemingly random fashion based on
the ordering of the selected task's child list.  Additionally, it is not
guaranteed at all to free a large amount of memory that we need to
prevent additional oom killing in the very near future.

Instead, we now only attempt to sacrifice the worst child not sharing its
parent's memory, if one exists.  The worst child is indicated with the
highest badness() score.  This serves two advantages: we kill a
memory-hogging task more often, and we allow the configurable
/proc/pid/oom_adj value to be considered as a factor in which child to
kill.

Reviewers may observe that the previous implementation would iterate
through the children and attempt to kill each until one was successful
and then the parent if none were found while the new code simply kills
the most memory-hogging task or the parent.  Note that the only time
oom_kill_task() fails, however, is when a child does not have an mm or
has a /proc/pid/oom_adj of OOM_DISABLE.  badness() returns 0 for both
cases, so the final oom_kill_task() will always succeed.

Acked-by: Rik van Riel <riel@redhat.com>
Acked-by: Nick Piggin <npiggin@suse.de>
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: David Rientjes <rientjes@google.com>
---
 mm/oom_kill.c |   23 +++++++++++++++++------
 1 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -432,7 +432,10 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
 			    unsigned long points, struct mem_cgroup *mem,
 			    const char *message)
 {
+	struct task_struct *victim = p;
 	struct task_struct *c;
+	unsigned long victim_points = 0;
+	struct timespec uptime;
 
 	if (printk_ratelimit())
 		dump_header(p, gfp_mask, order, mem);
@@ -446,19 +449,27 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
 		return 0;
 	}
 
-	printk(KERN_ERR "%s: kill process %d (%s) score %li or a child\n",
-					message, task_pid_nr(p), p->comm, points);
+	pr_err("%s: Kill process %d (%s) with score %lu or sacrifice child\n",
+		message, task_pid_nr(p), p->comm, points);
 
-	/* Try to kill a child first */
+	do_posix_clock_monotonic_gettime(&uptime);
+	/* Try to sacrifice the worst child first */
 	list_for_each_entry(c, &p->children, sibling) {
+		unsigned long cpoints;
+
 		if (c->mm == p->mm)
 			continue;
 		if (mem && !task_in_mem_cgroup(c, mem))
 			continue;
-		if (!oom_kill_task(c))
-			return 0;
+
+		/* badness() returns 0 if the thread is unkillable */
+		cpoints = badness(c, uptime.tv_sec);
+		if (cpoints > victim_points) {
+			victim = c;
+			victim_points = cpoints;
+		}
 	}
-	return oom_kill_task(p);
+	return oom_kill_task(victim);
 }
 
 #ifdef CONFIG_CGROUP_MEM_RES_CTLR

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[patch 03/10 -mm v3] oom: select task from tasklist for mempolicy ooms

[David Rientjes]

The oom killer presently kills current whenever there is no more memory
free or reclaimable on its mempolicy's nodes.  There is no guarantee that
current is a memory-hogging task or that killing it will free any
substantial amount of memory, however.

In such situations, it is better to scan the tasklist for nodes that are
allowed to allocate on current's set of nodes and kill the task with the
highest badness() score.  This ensures that the most memory-hogging task,
or the one configured by the user with /proc/pid/oom_adj, is always
selected in such scenarios.

It is necessary to synchronize the detachment of task->mempolicy with
task_lock(task) to ensure it is not prematurely destroyed while a user is
operating on it.

Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: David Rientjes <rientjes@google.com>
---
 include/linux/mempolicy.h |   13 +++++++-
 kernel/exit.c             |    8 ++--
 mm/mempolicy.c            |   44 +++++++++++++++++++++++++
 mm/oom_kill.c             |   77 +++++++++++++++++++++++++++-----------------
 4 files changed, 107 insertions(+), 35 deletions(-)

diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h
--- a/include/linux/mempolicy.h
+++ b/include/linux/mempolicy.h
@@ -202,6 +202,8 @@ extern struct zonelist *huge_zonelist(struct vm_area_struct *vma,
 				unsigned long addr, gfp_t gfp_flags,
 				struct mempolicy **mpol, nodemask_t **nodemask);
 extern bool init_nodemask_of_mempolicy(nodemask_t *mask);
+extern bool mempolicy_nodemask_intersects(struct task_struct *tsk,
+				const nodemask_t *mask);
 extern unsigned slab_node(struct mempolicy *policy);
 
 extern enum zone_type policy_zone;
@@ -329,7 +331,16 @@ static inline struct zonelist *huge_zonelist(struct vm_area_struct *vma,
 	return node_zonelist(0, gfp_flags);
 }
 
-static inline bool init_nodemask_of_mempolicy(nodemask_t *m) { return false; }
+static inline bool init_nodemask_of_mempolicy(nodemask_t *m)
+{
+	return false;
+}
+
+static inline bool mempolicy_nodemask_intersects(struct task_struct *tsk,
+			const nodemask_t *mask)
+{
+	return false;
+}
 
 static inline int do_migrate_pages(struct mm_struct *mm,
 			const nodemask_t *from_nodes,
diff --git a/kernel/exit.c b/kernel/exit.c
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -697,6 +697,10 @@ static void exit_mm(struct task_struct * tsk)
 	enter_lazy_tlb(mm, current);
 	/* We don't want this task to be frozen prematurely */
 	clear_freeze_flag(tsk);
+#ifdef CONFIG_NUMA
+	mpol_put(tsk->mempolicy);
+	tsk->mempolicy = NULL;
+#endif
 	task_unlock(tsk);
 	mm_update_next_owner(mm);
 	mmput(mm);
@@ -1001,10 +1005,6 @@ NORET_TYPE void do_exit(long code)
 	perf_event_exit_task(tsk);
 
 	exit_notify(tsk, group_dead);
-#ifdef CONFIG_NUMA
-	mpol_put(tsk->mempolicy);
-	tsk->mempolicy = NULL;
-#endif
 #ifdef CONFIG_FUTEX
 	if (unlikely(current->pi_state_cache))
 		kfree(current->pi_state_cache);
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1638,6 +1638,50 @@ bool init_nodemask_of_mempolicy(nodemask_t *mask)
 }
 #endif
 
+/*
+ * mempolicy_nodemask_intersects
+ *
+ * If tsk's mempolicy is "default" [NULL], return 'true' to indicate default
+ * policy.  Otherwise, check for intersection between mask and the policy
+ * nodemask for 'bind' or 'interleave' policy.  For 'perferred' or 'local'
+ * policy, always return true since it may allocate elsewhere on fallback.
+ *
+ * Takes task_lock(tsk) to prevent freeing of its mempolicy.
+ */
+bool mempolicy_nodemask_intersects(struct task_struct *tsk,
+					const nodemask_t *mask)
+{
+	struct mempolicy *mempolicy;
+	bool ret = true;
+
+	if (!mask)
+		return ret;
+	task_lock(tsk);
+	mempolicy = tsk->mempolicy;
+	if (!mempolicy)
+		goto out;
+
+	switch (mempolicy->mode) {
+	case MPOL_PREFERRED:
+		/*
+		 * MPOL_PREFERRED and MPOL_F_LOCAL are only preferred nodes to
+		 * allocate from, they may fallback to other nodes when oom.
+		 * Thus, it's possible for tsk to have allocated memory from
+		 * nodes in mask.
+		 */
+		break;
+	case MPOL_BIND:
+	case MPOL_INTERLEAVE:
+		ret = nodes_intersects(mempolicy->v.nodes, *mask);
+		break;
+	default:
+		BUG();
+	}
+out:
+	task_unlock(tsk);
+	return ret;
+}
+
 /* Allocate a page in interleaved policy.
    Own path because it needs to do special accounting. */
 static struct page *alloc_page_interleave(gfp_t gfp, unsigned order,
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -26,6 +26,7 @@
 #include <linux/module.h>
 #include <linux/notifier.h>
 #include <linux/memcontrol.h>
+#include <linux/mempolicy.h>
 #include <linux/security.h>
 
 int sysctl_panic_on_oom;
@@ -36,19 +37,35 @@ static DEFINE_SPINLOCK(zone_scan_lock);
 
 /*
  * Do all threads of the target process overlap our allowed nodes?
+ * @tsk: task struct of which task to consider
+ * @mask: nodemask passed to page allocator for mempolicy ooms
  */
-static int has_intersects_mems_allowed(struct task_struct *tsk)
+static bool has_intersects_mems_allowed(struct task_struct *tsk,
+						const nodemask_t *mask)
 {
-	struct task_struct *t;
+	struct task_struct *start = tsk;
 
-	t = tsk;
 	do {
-		if (cpuset_mems_allowed_intersects(current, t))
-			return 1;
-		t = next_thread(t);
-	} while (t != tsk);
-
-	return 0;
+		if (mask) {
+			/*
+			 * If this is a mempolicy constrained oom, tsk's
+			 * cpuset is irrelevant.  Only return true if its
+			 * mempolicy intersects current, otherwise it may be
+			 * needlessly killed.
+			 */
+			if (mempolicy_nodemask_intersects(tsk, mask))
+				return true;
+		} else {
+			/*
+			 * This is not a mempolicy constrained oom, so only
+			 * check the mems of tsk's cpuset.
+			 */
+			if (cpuset_mems_allowed_intersects(current, tsk))
+				return true;
+		}
+		tsk = next_thread(tsk);
+	} while (tsk != start);
+	return false;
 }
 
 /**
@@ -236,7 +253,8 @@ static enum oom_constraint constrained_alloc(struct zonelist *zonelist,
  * (not docbooked, we don't want this one cluttering up the manual)
  */
 static struct task_struct *select_bad_process(unsigned long *ppoints,
-						struct mem_cgroup *mem)
+		struct mem_cgroup *mem, enum oom_constraint constraint,
+		const nodemask_t *mask)
 {
 	struct task_struct *p;
 	struct task_struct *chosen = NULL;
@@ -258,7 +276,9 @@ static struct task_struct *select_bad_process(unsigned long *ppoints,
 			continue;
 		if (mem && !task_in_mem_cgroup(p, mem))
 			continue;
-		if (!has_intersects_mems_allowed(p))
+		if (!has_intersects_mems_allowed(p,
+				constraint == CONSTRAINT_MEMORY_POLICY ? mask :
+									 NULL))
 			continue;
 
 		/*
@@ -482,7 +502,7 @@ void mem_cgroup_out_of_memory(struct mem_cgroup *mem, gfp_t gfp_mask)
 		panic("out of memory(memcg). panic_on_oom is selected.\n");
 	read_lock(&tasklist_lock);
 retry:
-	p = select_bad_process(&points, mem);
+	p = select_bad_process(&points, mem, CONSTRAINT_NONE, NULL);
 	if (PTR_ERR(p) == -1UL)
 		goto out;
 
@@ -564,7 +584,8 @@ void clear_zonelist_oom(struct zonelist *zonelist, gfp_t gfp_mask)
 /*
  * Must be called with tasklist_lock held for read.
  */
-static void __out_of_memory(gfp_t gfp_mask, int order)
+static void __out_of_memory(gfp_t gfp_mask, int order,
+			enum oom_constraint constraint, const nodemask_t *mask)
 {
 	struct task_struct *p;
 	unsigned long points;
@@ -578,7 +599,7 @@ retry:
 	 * Rambo mode: Shoot down a process and hope it solves whatever
 	 * issues we may have.
 	 */
-	p = select_bad_process(&points, NULL);
+	p = select_bad_process(&points, NULL, constraint, mask);
 
 	if (PTR_ERR(p) == -1UL)
 		return;
@@ -612,7 +633,8 @@ void pagefault_out_of_memory(void)
 		panic("out of memory from page fault. panic_on_oom is selected.\n");
 
 	read_lock(&tasklist_lock);
-	__out_of_memory(0, 0); /* unknown gfp_mask and order */
+	/* unknown gfp_mask and order */
+	__out_of_memory(0, 0, CONSTRAINT_NONE, NULL);
 	read_unlock(&tasklist_lock);
 
 	/*
@@ -628,6 +650,7 @@ void pagefault_out_of_memory(void)
  * @zonelist: zonelist pointer
  * @gfp_mask: memory allocation flags
  * @order: amount of memory being requested as a power of 2
+ * @nodemask: nodemask passed to page allocator
  *
  * If we run out of memory, we have the choice between either
  * killing a random task (bad), letting the system crash (worse)
@@ -656,24 +679,18 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
 	 */
 	constraint = constrained_alloc(zonelist, gfp_mask, nodemask);
 	read_lock(&tasklist_lock);
-
-	switch (constraint) {
-	case CONSTRAINT_MEMORY_POLICY:
-		oom_kill_process(current, gfp_mask, order, 0, NULL,
-				"No available memory (MPOL_BIND)");
-		break;
-
-	case CONSTRAINT_NONE:
-		if (sysctl_panic_on_oom) {
+	if (unlikely(sysctl_panic_on_oom)) {
+		/*
+		 * panic_on_oom only affects CONSTRAINT_NONE, the kernel
+		 * should not panic for cpuset or mempolicy induced memory
+		 * failures.
+		 */
+		if (constraint == CONSTRAINT_NONE) {
 			dump_header(NULL, gfp_mask, order, NULL);
-			panic("out of memory. panic_on_oom is selected\n");
+			panic("Out of memory: panic_on_oom is enabled\n");
 		}
-		/* Fall-through */
-	case CONSTRAINT_CPUSET:
-		__out_of_memory(gfp_mask, order);
-		break;
 	}
-
+	__out_of_memory(gfp_mask, order, constraint, nodemask);
 	read_unlock(&tasklist_lock);
 
 	/*

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[patch 04/10 -mm v3] oom: remove special handling for pagefault ooms

[David Rientjes]

It is possible to remove the special pagefault oom handler by simply
oom locking all system zones and then calling directly into
out_of_memory().

All populated zones must have ZONE_OOM_LOCKED set, otherwise there is a
parallel oom killing in progress that will lead to eventual memory
freeing so it's not necessary to needlessly kill another task.  The
context in which the pagefault is allocating memory is unknown to the oom
killer, so this is done on a system-wide level.

If a task has already been oom killed and hasn't fully exited yet, this
will be a no-op since select_bad_process() recognizes tasks across the
system with TIF_MEMDIE set.

Signed-off-by: David Rientjes <rientjes@google.com>
---
 mm/oom_kill.c |   91 +++++++++++++++++++++++++++++++++++++--------------------
 1 files changed, 59 insertions(+), 32 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -582,6 +582,44 @@ void clear_zonelist_oom(struct zonelist *zonelist, gfp_t gfp_mask)
 }
 
 /*
+ * Try to acquire the oom killer lock for all system zones.  Returns zero if a
+ * parallel oom killing is taking place, otherwise locks all zones and returns
+ * non-zero.
+ */
+static int try_set_system_oom(void)
+{
+	struct zone *zone;
+	int ret = 1;
+
+	spin_lock(&zone_scan_lock);
+	for_each_populated_zone(zone)
+		if (zone_is_oom_locked(zone)) {
+			ret = 0;
+			goto out;
+		}
+	for_each_populated_zone(zone)
+		zone_set_flag(zone, ZONE_OOM_LOCKED);
+out:
+	spin_unlock(&zone_scan_lock);
+	return ret;
+}
+
+/*
+ * Clears ZONE_OOM_LOCKED for all system zones so that failed allocation
+ * attempts or page faults may now recall the oom killer, if necessary.
+ */
+static void clear_system_oom(void)
+{
+	struct zone *zone;
+
+	spin_lock(&zone_scan_lock);
+	for_each_populated_zone(zone)
+		zone_clear_flag(zone, ZONE_OOM_LOCKED);
+	spin_unlock(&zone_scan_lock);
+}
+
+
+/*
  * Must be called with tasklist_lock held for read.
  */
 static void __out_of_memory(gfp_t gfp_mask, int order,
@@ -616,38 +654,9 @@ retry:
 		goto retry;
 }
 
-/*
- * pagefault handler calls into here because it is out of memory but
- * doesn't know exactly how or why.
- */
-void pagefault_out_of_memory(void)
-{
-	unsigned long freed = 0;
-
-	blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
-	if (freed > 0)
-		/* Got some memory back in the last second. */
-		return;
-
-	if (sysctl_panic_on_oom)
-		panic("out of memory from page fault. panic_on_oom is selected.\n");
-
-	read_lock(&tasklist_lock);
-	/* unknown gfp_mask and order */
-	__out_of_memory(0, 0, CONSTRAINT_NONE, NULL);
-	read_unlock(&tasklist_lock);
-
-	/*
-	 * Give "p" a good chance of killing itself before we
-	 * retry to allocate memory.
-	 */
-	if (!test_thread_flag(TIF_MEMDIE))
-		schedule_timeout_uninterruptible(1);
-}
-
 /**
  * out_of_memory - kill the "best" process when we run out of memory
- * @zonelist: zonelist pointer
+ * @zonelist: zonelist pointer passed to page allocator
  * @gfp_mask: memory allocation flags
  * @order: amount of memory being requested as a power of 2
  * @nodemask: nodemask passed to page allocator
@@ -661,7 +670,7 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
 		int order, nodemask_t *nodemask)
 {
 	unsigned long freed = 0;
-	enum oom_constraint constraint;
+	enum oom_constraint constraint = CONSTRAINT_NONE;
 
 	blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
 	if (freed > 0)
@@ -677,7 +686,8 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
 	 * Check if there were limitations on the allocation (only relevant for
 	 * NUMA) that may require different handling.
 	 */
-	constraint = constrained_alloc(zonelist, gfp_mask, nodemask);
+	if (zonelist)
+		constraint = constrained_alloc(zonelist, gfp_mask, nodemask);
 	read_lock(&tasklist_lock);
 	if (unlikely(sysctl_panic_on_oom)) {
 		/*
@@ -687,6 +697,7 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
 		 */
 		if (constraint == CONSTRAINT_NONE) {
 			dump_header(NULL, gfp_mask, order, NULL);
+			read_unlock(&tasklist_lock);
 			panic("Out of memory: panic_on_oom is enabled\n");
 		}
 	}
@@ -700,3 +711,19 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
 	if (!test_thread_flag(TIF_MEMDIE))
 		schedule_timeout_uninterruptible(1);
 }
+
+/*
+ * The pagefault handler calls here because it is out of memory, so kill a
+ * memory-hogging task.  If a populated zone has ZONE_OOM_LOCKED set, a parallel
+ * oom killing is already in progress so do nothing.  If a task is found with
+ * TIF_MEMDIE set, it has been killed so do nothing and allow it to exit.
+ */
+void pagefault_out_of_memory(void)
+{
+	if (try_set_system_oom()) {
+		out_of_memory(NULL, 0, 0, NULL);
+		clear_system_oom();
+	}
+	if (!test_thread_flag(TIF_MEMDIE))
+		schedule_timeout_uninterruptible(1);
+}

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[patch 05/10 -mm v3] oom: badness heuristic rewrite

[David Rientjes]

This a complete rewrite of the oom killer's badness() heuristic which is
used to determine which task to kill in oom conditions.  The goal is to
make it as simple and predictable as possible so the results are better
understood and we end up killing the task which will lead to the most
memory freeing while still respecting the fine-tuning from userspace.

The baseline for the heuristic is a proportion of memory that each task
is currently using in memory plus swap compared to the amount of
"allowable" memory.  "Allowable," in this sense, means the system-wide
resources for unconstrained oom conditions, the set of mempolicy nodes,
the mems attached to current's cpuset, or a memory controller's limit.
The proportion is given on a scale of 0 (never kill) to 1000 (always
kill), roughly meaning that if a task has a badness() score of 500 that
the task consumes approximately 50% of allowable memory resident in RAM
or in swap space.

The proportion is always relative to the amount of "allowable" memory and
not the total amount of RAM systemwide so that mempolicies and cpusets
may operate in isolation; they shall not need to know the true size of
the machine on which they are running if they are bound to a specific set
of nodes or mems, respectively.

Forkbomb detection is done in a completely different way: a threshold is
configurable from userspace to determine how many first-generation execve
children (those with their own address spaces) a task may have before it
is considered a forkbomb.  This can be tuned by altering the value in
/proc/sys/vm/oom_forkbomb_thres, which defaults to 1000.

When a task has more than 1000 first-generation children with different
address spaces than itself, a penalty of

	(average rss of children) * (# of 1st generation execve children)
	-----------------------------------------------------------------
			oom_forkbomb_thres

is assessed.  So, for example, using the default oom_forkbomb_thres of
1000, the penalty is twice the average rss of all its execve children if
there are 2000 such tasks.  A task is considered to count toward the
threshold if its total runtime is less than one second; for 1000 of such
tasks to exist, the parent process must be forking at an extremely high
rate either erroneously or maliciously.

Even though a particular task may be designated a forkbomb and selected
as the victim, the oom killer will still kill the 1st generation execve
child with the highest badness() score in its place.  The avoids killing
important servers or system daemons.  When a web server forks a very
large number of threads for client connections, for example, it is much
better to kill one of those threads than to kill the server and make it
unresponsive.

Root tasks are given 3% extra memory just like __vm_enough_memory()
provides in LSMs.  In the event of two tasks consuming similar amounts of
memory, it is generally better to save root's task.

Because of the change in the badness() heuristic's baseline, it is also
necessary to introduce a new user interface to tune it.  It's not
possible to redefine the meaning of /proc/pid/oom_adj with a new scale
since the ABI cannot be changed for backward compatability.  Instead, a
new tunable, /proc/pid/oom_score_adj, is added that ranges from -1000 to
+1000.  It may be used to polarize the heuristic such that certain tasks
are never considered for oom kill while others may always be considered.
The value is added directory into the badness() score so a value of -500,
for example, means to discount 50% of its memory consumption in
comparison to other tasks either on the system, bound to the mempolicy,
in the cpuset, or sharing the same memory controller.

/proc/pid/oom_adj is changed so that its meaning is rescaled into the
units used by /proc/pid/oom_score_adj, and vice versa.  Changing one of
these per-task tunables will rescale the value of the other to an
equivalent meaning.  Although /proc/pid/oom_adj was originally defined as
a bitshift on the badness score, it now shares the same linear growth as
/proc/pid/oom_score_adj but with different granularity.  This is required
so the ABI is not broken with userspace applications and allows oom_adj
to be deprecated for future removal.

Signed-off-by: David Rientjes <rientjes@google.com>
---
 Documentation/filesystems/proc.txt |   97 +++++++----
 Documentation/sysctl/vm.txt        |   21 +++
 fs/proc/base.c                     |   98 +++++++++++-
 include/linux/memcontrol.h         |    8 +
 include/linux/oom.h                |   18 ++-
 include/linux/sched.h              |    3 +-
 kernel/fork.c                      |    1 +
 kernel/sysctl.c                    |    8 +
 mm/memcontrol.c                    |    8 +
 mm/oom_kill.c                      |  319 ++++++++++++++++++++----------------
 10 files changed, 395 insertions(+), 186 deletions(-)

diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -33,7 +33,8 @@ Table of Contents
   2	Modifying System Parameters
 
   3	Per-Process Parameters
-  3.1	/proc/<pid>/oom_adj - Adjust the oom-killer score
+  3.1	/proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj - Adjust the oom-killer
+								score
   3.2	/proc/<pid>/oom_score - Display current oom-killer score
   3.3	/proc/<pid>/io - Display the IO accounting fields
   3.4	/proc/<pid>/coredump_filter - Core dump filtering settings
@@ -1236,42 +1237,64 @@ of the kernel.
 CHAPTER 3: PER-PROCESS PARAMETERS
 ------------------------------------------------------------------------------
 
-3.1 /proc/<pid>/oom_adj - Adjust the oom-killer score
-------------------------------------------------------
-
-This file can be used to adjust the score used to select which processes
-should be killed in an  out-of-memory  situation.  Giving it a high score will
-increase the likelihood of this process being killed by the oom-killer.  Valid
-values are in the range -16 to +15, plus the special value -17, which disables
-oom-killing altogether for this process.
-
-The process to be killed in an out-of-memory situation is selected among all others
-based on its badness score. This value equals the original memory size of the process
-and is then updated according to its CPU time (utime + stime) and the
-run time (uptime - start time). The longer it runs the smaller is the score.
-Badness score is divided by the square root of the CPU time and then by
-the double square root of the run time.
-
-Swapped out tasks are killed first. Half of each child's memory size is added to
-the parent's score if they do not share the same memory. Thus forking servers
-are the prime candidates to be killed. Having only one 'hungry' child will make
-parent less preferable than the child.
-
-/proc/<pid>/oom_score shows process' current badness score.
-
-The following heuristics are then applied:
- * if the task was reniced, its score doubles
- * superuser or direct hardware access tasks (CAP_SYS_ADMIN, CAP_SYS_RESOURCE
- 	or CAP_SYS_RAWIO) have their score divided by 4
- * if oom condition happened in one cpuset and checked process does not belong
- 	to it, its score is divided by 8
- * the resulting score is multiplied by two to the power of oom_adj, i.e.
-	points <<= oom_adj when it is positive and
-	points >>= -(oom_adj) otherwise
-
-The task with the highest badness score is then selected and its children
-are killed, process itself will be killed in an OOM situation when it does
-not have children or some of them disabled oom like described above.
+3.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score
+--------------------------------------------------------------------------------
+
+These file can be used to adjust the badness heuristic used to select which
+process gets killed in out of memory conditions.
+
+The badness heuristic assigns a value to each candidate task ranging from 0
+(never kill) to 1000 (always kill) to determine which process is targeted.  The
+units are roughly a proportion along that range of allowed memory the process
+may allocate from based on an estimation of its current memory and swap use.
+For example, if a task is using all allowed memory, its badness score will be
+1000.  If it is using half of its allowed memory, its score will be 500.
+
+There are a couple of additional factors included in the badness score: root
+processes are given 3% extra memory over other tasks, and tasks which forkbomb
+an excessive number of child processes are penalized by their average size.
+The number of child processes considered to be a forkbomb is configurable
+via /proc/sys/vm/oom_forkbomb_thres (see Documentation/sysctl/vm.txt).
+
+The amount of "allowed" memory depends on the context in which the oom killer
+was called.  If it is due to the memory assigned to the allocating task's cpuset
+being exhausted, the allowed memory represents the set of mems assigned to that
+cpuset.  If it is due to a mempolicy's node(s) being exhausted, the allowed
+memory represents the set of mempolicy nodes.  If it is due to a memory
+limit (or swap limit) being reached, the allowed memory is that configured
+limit.  Finally, if it is due to the entire system being out of memory, the
+allowed memory represents all allocatable resources.
+
+The value of /proc/<pid>/oom_score_adj is added to the badness score before it
+is used to determine which task to kill.  Acceptable values range from -1000
+(OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX).  This allows userspace to
+polarize the preference for oom killing either by always preferring a certain
+task or completely disabling it.  The lowest possible value, -1000, is
+equivalent to disabling oom killing entirely for that task since it will always
+report a badness score of 0.
+
+Consequently, it is very simple for userspace to define the amount of memory to
+consider for each task.  Setting a /proc/<pid>/oom_score_adj value of +500, for
+example, is roughly equivalent to allowing the remainder of tasks sharing the
+same system, cpuset, mempolicy, or memory controller resources to use at least
+50% more memory.  A value of -500, on the other hand, would be roughly
+equivalent to discounting 50% of the task's allowed memory from being considered
+as scoring against the task.
+
+For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also
+be used to tune the badness score.  Its acceptable values range from -16
+(OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17
+(OOM_DISABLE) to disable oom killing entirely for that task.  Its value is
+scaled linearly with /proc/<pid>/oom_score_adj.
+
+Writing to /proc/<pid>/oom_score_adj or /proc/<pid>/oom_adj will change the
+other with its scaled value.
+
+Caveat: when a parent task is selected, the oom killer will sacrifice any first
+generation children with seperate address spaces instead, if possible.  This
+avoids servers and important system daemons from being killed and loses the
+minimal amount of work.
+
 
 3.2 /proc/<pid>/oom_score - Display current oom-killer score
 -------------------------------------------------------------
diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
--- a/Documentation/sysctl/vm.txt
+++ b/Documentation/sysctl/vm.txt
@@ -44,6 +44,7 @@ Currently, these files are in /proc/sys/vm:
 - nr_trim_pages         (only if CONFIG_MMU=n)
 - numa_zonelist_order
 - oom_dump_tasks
+- oom_forkbomb_thres
 - oom_kill_allocating_task
 - overcommit_memory
 - overcommit_ratio
@@ -490,6 +491,26 @@ The default value is 0.
 
 ==============================================================
 
+oom_forkbomb_thres
+
+This value defines how many children with a seperate address space a specific
+task may have before being considered as a possible forkbomb.  Tasks with more
+children not sharing the same address space as the parent will be penalized by a
+quantity of memory equaling
+
+	(average rss of execve children) * (# of 1st generation execve children)
+	------------------------------------------------------------------------
+				oom_forkbomb_thres
+
+in the oom killer's badness heuristic.  Such tasks may be protected with a lower
+oom_adj value (see Documentation/filesystems/proc.txt) if necessary.
+
+A value of 0 will disable forkbomb detection.
+
+The default value is 1000.
+
+==============================================================
+
 oom_kill_allocating_task
 
 This enables or disables killing the OOM-triggering task in
diff --git a/fs/proc/base.c b/fs/proc/base.c
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -81,6 +81,7 @@
 #include <linux/elf.h>
 #include <linux/pid_namespace.h>
 #include <linux/fs_struct.h>
+#include <linux/swap.h>
 #include "internal.h"
 
 /* NOTE:
@@ -439,7 +440,6 @@ static const struct file_operations proc_lstats_operations = {
 #endif
 
 /* The badness from the OOM killer */
-unsigned long badness(struct task_struct *p, unsigned long uptime);
 static int proc_oom_score(struct task_struct *task, char *buffer)
 {
 	unsigned long points;
@@ -447,7 +447,13 @@ static int proc_oom_score(struct task_struct *task, char *buffer)
 
 	do_posix_clock_monotonic_gettime(&uptime);
 	read_lock(&tasklist_lock);
-	points = badness(task->group_leader, uptime.tv_sec);
+	points = oom_badness(task->group_leader,
+				global_page_state(NR_INACTIVE_ANON) +
+				global_page_state(NR_ACTIVE_ANON) +
+				global_page_state(NR_INACTIVE_FILE) +
+				global_page_state(NR_ACTIVE_FILE) +
+				total_swap_pages,
+				uptime.tv_sec);
 	read_unlock(&tasklist_lock);
 	return sprintf(buffer, "%lu\n", points);
 }
@@ -1133,7 +1139,15 @@ static ssize_t oom_adjust_write(struct file *file, const char __user *buf,
 	}
 
 	task->signal->oom_adj = oom_adjust;
-
+	/*
+	 * Scale /proc/pid/oom_score_adj appropriately ensuring that a maximum
+	 * value is always attainable.
+	 */
+	if (task->signal->oom_adj == OOM_ADJUST_MAX)
+		task->signal->oom_score_adj = OOM_SCORE_ADJ_MAX;
+	else
+		task->signal->oom_score_adj = (oom_adjust * OOM_SCORE_ADJ_MAX) /
+								-OOM_DISABLE;
 	unlock_task_sighand(task, &flags);
 	put_task_struct(task);
 
@@ -1145,6 +1159,82 @@ static const struct file_operations proc_oom_adjust_operations = {
 	.write		= oom_adjust_write,
 };
 
+static ssize_t oom_score_adj_read(struct file *file, char __user *buf,
+					size_t count, loff_t *ppos)
+{
+	struct task_struct *task = get_proc_task(file->f_path.dentry->d_inode);
+	char buffer[PROC_NUMBUF];
+	int oom_score_adj = OOM_SCORE_ADJ_MIN;
+	unsigned long flags;
+	size_t len;
+
+	if (!task)
+		return -ESRCH;
+	if (lock_task_sighand(task, &flags)) {
+		oom_score_adj = task->signal->oom_score_adj;
+		unlock_task_sighand(task, &flags);
+	}
+	put_task_struct(task);
+	len = snprintf(buffer, sizeof(buffer), "%d\n", oom_score_adj);
+	return simple_read_from_buffer(buf, count, ppos, buffer, len);
+}
+
+static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
+					size_t count, loff_t *ppos)
+{
+	struct task_struct *task;
+	char buffer[PROC_NUMBUF];
+	unsigned long flags;
+	long oom_score_adj;
+	int err;
+
+	memset(buffer, 0, sizeof(buffer));
+	if (count > sizeof(buffer) - 1)
+		count = sizeof(buffer) - 1;
+	if (copy_from_user(buffer, buf, count))
+		return -EFAULT;
+
+	err = strict_strtol(strstrip(buffer), 0, &oom_score_adj);
+	if (err)
+		return -EINVAL;
+	if (oom_score_adj < OOM_SCORE_ADJ_MIN ||
+			oom_score_adj > OOM_SCORE_ADJ_MAX)
+		return -EINVAL;
+
+	task = get_proc_task(file->f_path.dentry->d_inode);
+	if (!task)
+		return -ESRCH;
+	if (!lock_task_sighand(task, &flags)) {
+		put_task_struct(task);
+		return -ESRCH;
+	}
+	if (oom_score_adj < task->signal->oom_score_adj &&
+			!capable(CAP_SYS_RESOURCE)) {
+		unlock_task_sighand(task, &flags);
+		put_task_struct(task);
+		return -EACCES;
+	}
+
+	task->signal->oom_score_adj = oom_score_adj;
+	/*
+	 * Scale /proc/pid/oom_adj appropriately ensuring that OOM_DISABLE is
+	 * always attainable.
+	 */
+	if (task->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
+		task->signal->oom_adj = OOM_DISABLE;
+	else
+		task->signal->oom_adj = (oom_score_adj * OOM_ADJUST_MAX) /
+							OOM_SCORE_ADJ_MAX;
+	unlock_task_sighand(task, &flags);
+	put_task_struct(task);
+	return count;
+}
+
+static const struct file_operations proc_oom_score_adj_operations = {
+	.read		= oom_score_adj_read,
+	.write		= oom_score_adj_write,
+};
+
 #ifdef CONFIG_AUDITSYSCALL
 #define TMPBUFLEN 21
 static ssize_t proc_loginuid_read(struct file * file, char __user * buf,
@@ -2712,6 +2802,7 @@ static const struct pid_entry tgid_base_stuff[] = {
 #endif
 	INF("oom_score",  S_IRUGO, proc_oom_score),
 	REG("oom_adj",    S_IRUGO|S_IWUSR, proc_oom_adjust_operations),
+	REG("oom_score_adj", S_IRUGO|S_IWUSR, proc_oom_score_adj_operations),
 #ifdef CONFIG_AUDITSYSCALL
 	REG("loginuid",   S_IWUSR|S_IRUGO, proc_loginuid_operations),
 	REG("sessionid",  S_IRUGO, proc_sessionid_operations),
@@ -3046,6 +3137,7 @@ static const struct pid_entry tid_base_stuff[] = {
 #endif
 	INF("oom_score", S_IRUGO, proc_oom_score),
 	REG("oom_adj",   S_IRUGO|S_IWUSR, proc_oom_adjust_operations),
+	REG("oom_score_adj", S_IRUGO|S_IWUSR, proc_oom_score_adj_operations),
 #ifdef CONFIG_AUDITSYSCALL
 	REG("loginuid",  S_IWUSR|S_IRUGO, proc_loginuid_operations),
 	REG("sessionid",  S_IRUSR, proc_sessionid_operations),
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -128,6 +128,8 @@ void mem_cgroup_update_file_mapped(struct page *page, int val);
 unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
 						gfp_t gfp_mask, int nid,
 						int zid);
+u64 mem_cgroup_get_limit(struct mem_cgroup *mem);
+
 #else /* CONFIG_CGROUP_MEM_RES_CTLR */
 struct mem_cgroup;
 
@@ -306,6 +308,12 @@ unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
 	return 0;
 }
 
+static inline
+u64 mem_cgroup_get_limit(struct mem_cgroup *mem)
+{
+	return 0;
+}
+
 #endif /* CONFIG_CGROUP_MEM_CONT */
 
 #endif /* _LINUX_MEMCONTROL_H */
diff --git a/include/linux/oom.h b/include/linux/oom.h
--- a/include/linux/oom.h
+++ b/include/linux/oom.h
@@ -1,14 +1,27 @@
 #ifndef __INCLUDE_LINUX_OOM_H
 #define __INCLUDE_LINUX_OOM_H
 
-/* /proc/<pid>/oom_adj set to -17 protects from the oom-killer */
+/*
+ * /proc/<pid>/oom_adj set to -17 protects from the oom-killer
+ */
 #define OOM_DISABLE (-17)
 /* inclusive */
 #define OOM_ADJUST_MIN (-16)
 #define OOM_ADJUST_MAX 15
 
+/*
+ * /proc/<pid>/oom_score_adj set to OOM_SCORE_ADJ_MIN disables oom killing for
+ * pid.
+ */
+#define OOM_SCORE_ADJ_MIN	(-1000)
+#define OOM_SCORE_ADJ_MAX	1000
+
+/* See Documentation/sysctl/vm.txt */
+#define DEFAULT_OOM_FORKBOMB_THRES	1000
+
 #ifdef __KERNEL__
 
+#include <linux/sched.h>
 #include <linux/types.h>
 #include <linux/nodemask.h>
 
@@ -24,6 +37,8 @@ enum oom_constraint {
 	CONSTRAINT_MEMORY_POLICY,
 };
 
+extern unsigned int oom_badness(struct task_struct *p,
+			unsigned long totalpages, unsigned long uptime);
 extern int try_set_zone_oom(struct zonelist *zonelist, gfp_t gfp_flags);
 extern void clear_zonelist_oom(struct zonelist *zonelist, gfp_t gfp_flags);
 
@@ -47,6 +62,7 @@ static inline void oom_killer_enable(void)
 extern int sysctl_panic_on_oom;
 extern int sysctl_oom_kill_allocating_task;
 extern int sysctl_oom_dump_tasks;
+extern int sysctl_oom_forkbomb_thres;
 
 #endif /* __KERNEL__*/
 #endif /* _INCLUDE_LINUX_OOM_H */
diff --git a/include/linux/sched.h b/include/linux/sched.h
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -624,7 +624,8 @@ struct signal_struct {
 	struct tty_audit_buf *tty_audit_buf;
 #endif
 
-	int oom_adj;	/* OOM kill score adjustment (bit shift) */
+	int oom_adj;		/* OOM kill score adjustment (bit shift) */
+	int oom_score_adj;	/* OOM kill score adjustment */
 };
 
 /* Context switch must be unlocked if interrupts are to be enabled */
diff --git a/kernel/fork.c b/kernel/fork.c
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -879,6 +879,7 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
 	tty_audit_fork(sig);
 
 	sig->oom_adj = current->signal->oom_adj;
+	sig->oom_score_adj = current->signal->oom_score_adj;
 
 	return 0;
 }
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -954,6 +954,14 @@ static struct ctl_table vm_table[] = {
 		.proc_handler	= proc_dointvec,
 	},
 	{
+		.procname	= "oom_forkbomb_thres",
+		.data		= &sysctl_oom_forkbomb_thres,
+		.maxlen		= sizeof(sysctl_oom_forkbomb_thres),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= &zero,
+	},
+	{
 		.procname	= "overcommit_ratio",
 		.data		= &sysctl_overcommit_ratio,
 		.maxlen		= sizeof(sysctl_overcommit_ratio),
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1119,6 +1119,14 @@ static int mem_cgroup_count_children(struct mem_cgroup *mem)
 }
 
 /*
+ * Return the memory + swap limit for a memcg.
+ */
+u64 mem_cgroup_get_limit(struct mem_cgroup *memcg)
+{
+	return res_counter_read_u64(&memcg->memsw, RES_LIMIT);
+}
+
+/*
  * Visit the first child (need not be the first child as per the ordering
  * of the cgroup list, since we track last_scanned_child) of @mem and use
  * that to reclaim free pages from.
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -4,6 +4,8 @@
  *  Copyright (C)  1998,2000  Rik van Riel
  *	Thanks go out to Claus Fischer for some serious inspiration and
  *	for goading me into coding this file...
+ *  Copyright (C)  2010  Google, Inc
+ *	Rewritten by David Rientjes
  *
  *  The routines in this file are used to kill a process when
  *  we're seriously out of memory. This gets called from __alloc_pages()
@@ -32,8 +34,8 @@
 int sysctl_panic_on_oom;
 int sysctl_oom_kill_allocating_task;
 int sysctl_oom_dump_tasks;
+int sysctl_oom_forkbomb_thres = DEFAULT_OOM_FORKBOMB_THRES;
 static DEFINE_SPINLOCK(zone_scan_lock);
-/* #define DEBUG */
 
 /*
  * Do all threads of the target process overlap our allowed nodes?
@@ -68,138 +70,129 @@ static bool has_intersects_mems_allowed(struct task_struct *tsk,
 	return false;
 }
 
-/**
- * badness - calculate a numeric value for how bad this task has been
- * @p: task struct of which task we should calculate
- * @uptime: current uptime in seconds
+/*
+ * Tasks that fork a very large number of children with seperate address spaces
+ * may be the result of a bug, user error, malicious applications, or even those
+ * with a very legitimate purpose.  The oom killer assesses a penalty equaling
  *
- * The formula used is relatively simple and documented inline in the
- * function. The main rationale is that we want to select a good task
- * to kill when we run out of memory.
+ *	(average rss of children) * (# of 1st generation execve children)
+ *	-----------------------------------------------------------------
+ *			sysctl_oom_forkbomb_thres
  *
- * Good in this context means that:
- * 1) we lose the minimum amount of work done
- * 2) we recover a large amount of memory
- * 3) we don't kill anything innocent of eating tons of memory
- * 4) we want to kill the minimum amount of processes (one)
- * 5) we try to kill the process the user expects us to kill, this
- *    algorithm has been meticulously tuned to meet the principle
- *    of least surprise ... (be careful when you change it)
+ * for such tasks to target the parent.  oom_kill_process() will attempt to
+ * first kill a child, so there's no risk of killing an important system daemon
+ * via this method.  A web server, for example, may fork a very large number of
+ * threads to response to client connections; it's much better to kill a child
+ * than to kill the parent, making the server unresponsive.  The goal here is
+ * to give the user a chance to recover from the error rather than deplete all
+ * memory such that the system is unusable, it's not meant to effect a forkbomb
+ * policy.
  */
-
-unsigned long badness(struct task_struct *p, unsigned long uptime)
+static unsigned long oom_forkbomb_penalty(struct task_struct *tsk)
 {
-	unsigned long points, cpu_time, run_time;
-	struct mm_struct *mm;
 	struct task_struct *child;
-	int oom_adj = p->signal->oom_adj;
-	struct task_cputime task_time;
-	unsigned long utime;
-	unsigned long stime;
+	unsigned long child_rss = 0;
+	int forkcount = 0;
 
-	if (oom_adj == OOM_DISABLE)
+	if (!sysctl_oom_forkbomb_thres)
 		return 0;
+	list_for_each_entry(child, &tsk->children, sibling) {
+		struct task_cputime task_time;
+		unsigned long runtime;
 
-	task_lock(p);
-	mm = p->mm;
-	if (!mm) {
-		task_unlock(p);
-		return 0;
+		task_lock(child);
+		if (!child->mm || child->mm == tsk->mm) {
+			task_unlock(child);
+			continue;
+		}
+		thread_group_cputime(child, &task_time);
+		runtime = cputime_to_jiffies(task_time.utime) +
+			  cputime_to_jiffies(task_time.stime);
+		/*
+		 * Only threads that have run for less than a second are
+		 * considered toward the forkbomb penalty, these threads rarely
+		 * get to execute at all in such cases anyway.
+		 */
+		if (runtime < HZ) {
+			child_rss += get_mm_rss(child->mm);
+			forkcount++;
+		}
+		task_unlock(child);
 	}
 
 	/*
-	 * The memory size of the process is the basis for the badness.
+	 * Forkbombs get penalized by:
+	 *
+	 * (average rss of children) * (# of first-generation execve children) /
+	 *			sysctl_oom_forkbomb_thres
 	 */
-	points = mm->total_vm;
+	return forkcount > sysctl_oom_forkbomb_thres ?
+				(child_rss / sysctl_oom_forkbomb_thres) : 0;
+}
+
+/**
+ * oom_badness - heuristic function to determine which candidate task to kill
+ * @p: task struct of which task we should calculate
+ * @totalpages: total present RAM allowed for page allocation
+ * @uptime: current uptime in seconds
+ *
+ * The heuristic for determining which task to kill is made to be as simple and
+ * predictable as possible.  The goal is to return the highest value for the
+ * task consuming the most memory to avoid subsequent oom conditions.
+ */
+unsigned int oom_badness(struct task_struct *p, unsigned long totalpages,
+							unsigned long uptime)
+{
+	struct mm_struct *mm;
+	int points;
 
 	/*
-	 * After this unlock we can no longer dereference local variable `mm'
+	 * Shortcut check for OOM_SCORE_ADJ_MIN so the entire heuristic doesn't
+	 * need to be executed for something that can't be killed.
 	 */
-	task_unlock(p);
+	if (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
+		return 0;
 
 	/*
-	 * swapoff can easily use up all memory, so kill those first.
+	 * When the PF_OOM_ORIGIN bit is set, it indicates the task should have
+	 * priority for oom killing.
 	 */
 	if (p->flags & PF_OOM_ORIGIN)
-		return ULONG_MAX;
+		return 1000;
 
-	/*
-	 * Processes which fork a lot of child processes are likely
-	 * a good choice. We add half the vmsize of the children if they
-	 * have an own mm. This prevents forking servers to flood the
-	 * machine with an endless amount of children. In case a single
-	 * child is eating the vast majority of memory, adding only half
-	 * to the parents will make the child our kill candidate of choice.
-	 */
-	list_for_each_entry(child, &p->children, sibling) {
-		task_lock(child);
-		if (child->mm != mm && child->mm)
-			points += child->mm->total_vm/2 + 1;
-		task_unlock(child);
+	task_lock(p);
+	mm = p->mm;
+	if (!mm) {
+		task_unlock(p);
+		return 0;
 	}
 
 	/*
-	 * CPU time is in tens of seconds and run time is in thousands
-         * of seconds. There is no particular reason for this other than
-         * that it turned out to work very well in practice.
+	 * The baseline for the badness score is the proportion of RAM that each
+	 * task's rss and swap space use.
 	 */
-	thread_group_cputime(p, &task_time);
-	utime = cputime_to_jiffies(task_time.utime);
-	stime = cputime_to_jiffies(task_time.stime);
-	cpu_time = (utime + stime) >> (SHIFT_HZ + 3);
-
-
-	if (uptime >= p->start_time.tv_sec)
-		run_time = (uptime - p->start_time.tv_sec) >> 10;
-	else
-		run_time = 0;
-
-	if (cpu_time)
-		points /= int_sqrt(cpu_time);
-	if (run_time)
-		points /= int_sqrt(int_sqrt(run_time));
-
-	/*
-	 * Niced processes are most likely less important, so double
-	 * their badness points.
-	 */
-	if (task_nice(p) > 0)
-		points *= 2;
-
-	/*
-	 * Superuser processes are usually more important, so we make it
-	 * less likely that we kill those.
-	 */
-	if (has_capability_noaudit(p, CAP_SYS_ADMIN) ||
-	    has_capability_noaudit(p, CAP_SYS_RESOURCE))
-		points /= 4;
+	points = (get_mm_rss(mm) + get_mm_counter(mm, MM_SWAPENTS)) * 1000 /
+			totalpages;
+	task_unlock(p);
+	points += oom_forkbomb_penalty(p);
 
 	/*
-	 * We don't want to kill a process with direct hardware access.
-	 * Not only could that mess up the hardware, but usually users
-	 * tend to only have this flag set on applications they think
-	 * of as important.
+	 * Root processes get 3% bonus, just like the __vm_enough_memory() used
+	 * by LSMs.
 	 */
-	if (has_capability_noaudit(p, CAP_SYS_RAWIO))
-		points /= 4;
+	if (has_capability_noaudit(p, CAP_SYS_ADMIN))
+		points -= 30;
 
 	/*
-	 * Adjust the score by oom_adj.
+	 * /proc/pid/oom_score_adj ranges from -1000 to +1000 such that the
+	 * range may either completely disable oom killing or always prefer a
+	 * certain task.
 	 */
-	if (oom_adj) {
-		if (oom_adj > 0) {
-			if (!points)
-				points = 1;
-			points <<= oom_adj;
-		} else
-			points >>= -(oom_adj);
-	}
+	points += p->signal->oom_score_adj;
 
-#ifdef DEBUG
-	printk(KERN_DEBUG "OOMkill: task %d (%s) got %lu points\n",
-	p->pid, p->comm, points);
-#endif
-	return points;
+	if (points < 0)
+		return 0;
+	return (points <= 1000) ? points : 1000;
 }
 
 /*
@@ -207,12 +200,24 @@ unsigned long badness(struct task_struct *p, unsigned long uptime)
  */
 #ifdef CONFIG_NUMA
 static enum oom_constraint constrained_alloc(struct zonelist *zonelist,
-				    gfp_t gfp_mask, nodemask_t *nodemask)
+				gfp_t gfp_mask, nodemask_t *nodemask,
+				unsigned long *totalpages)
 {
 	struct zone *zone;
 	struct zoneref *z;
 	enum zone_type high_zoneidx = gfp_zone(gfp_mask);
+	bool cpuset_limited = false;
+	int nid;
+
+	/* Default to all anonymous memory, page cache, and swap */
+	*totalpages = global_page_state(NR_INACTIVE_ANON) +
+			global_page_state(NR_ACTIVE_ANON) +
+			global_page_state(NR_INACTIVE_FILE) +
+			global_page_state(NR_ACTIVE_FILE) +
+			total_swap_pages;
 
+	if (!zonelist)
+		return CONSTRAINT_NONE;
 	/*
 	 * Reach here only when __GFP_NOFAIL is used. So, we should avoid
 	 * to kill current.We have to random task kill in this case.
@@ -222,26 +227,47 @@ static enum oom_constraint constrained_alloc(struct zonelist *zonelist,
 		return CONSTRAINT_NONE;
 
 	/*
-	 * The nodemask here is a nodemask passed to alloc_pages(). Now,
-	 * cpuset doesn't use this nodemask for its hardwall/softwall/hierarchy
-	 * feature. mempolicy is an only user of nodemask here.
-	 * check mempolicy's nodemask contains all N_HIGH_MEMORY
+	 * This is not a __GFP_THISNODE allocation, so a truncated nodemask in
+	 * the page allocator means a mempolicy is in effect.  Cpuset policy
+	 * is enforced in get_page_from_freelist().
 	 */
-	if (nodemask && !nodes_subset(node_states[N_HIGH_MEMORY], *nodemask))
+	if (nodemask && !nodes_subset(node_states[N_HIGH_MEMORY], *nodemask)) {
+		*totalpages = total_swap_pages;
+		for_each_node_mask(nid, *nodemask)
+			*totalpages += node_page_state(nid, NR_INACTIVE_ANON) +
+					node_page_state(nid, NR_ACTIVE_ANON) +
+					node_page_state(nid, NR_INACTIVE_FILE) +
+					node_page_state(nid, NR_ACTIVE_FILE);
 		return CONSTRAINT_MEMORY_POLICY;
+	}
 
 	/* Check this allocation failure is caused by cpuset's wall function */
 	for_each_zone_zonelist_nodemask(zone, z, zonelist,
 			high_zoneidx, nodemask)
 		if (!cpuset_zone_allowed_softwall(zone, gfp_mask))
-			return CONSTRAINT_CPUSET;
-
+			cpuset_limited = true;
+
+	if (cpuset_limited) {
+		*totalpages = total_swap_pages;
+		for_each_node_mask(nid, cpuset_current_mems_allowed)
+			*totalpages += node_page_state(nid, NR_INACTIVE_ANON) +
+					node_page_state(nid, NR_ACTIVE_ANON) +
+					node_page_state(nid, NR_INACTIVE_FILE) +
+					node_page_state(nid, NR_ACTIVE_FILE);
+		return CONSTRAINT_CPUSET;
+	}
 	return CONSTRAINT_NONE;
 }
 #else
 static enum oom_constraint constrained_alloc(struct zonelist *zonelist,
-				gfp_t gfp_mask, nodemask_t *nodemask)
+				gfp_t gfp_mask, nodemask_t *nodemask,
+				unsigned long *totalpages)
 {
+	*totalpages = global_page_state(NR_INACTIVE_ANON) +
+			global_page_state(NR_ACTIVE_ANON) +
+			global_page_state(NR_INACTIVE_FILE) +
+			global_page_state(NR_ACTIVE_FILE) +
+			total_swap_pages;
 	return CONSTRAINT_NONE;
 }
 #endif
@@ -252,9 +278,9 @@ static enum oom_constraint constrained_alloc(struct zonelist *zonelist,
  *
  * (not docbooked, we don't want this one cluttering up the manual)
  */
-static struct task_struct *select_bad_process(unsigned long *ppoints,
-		struct mem_cgroup *mem, enum oom_constraint constraint,
-		const nodemask_t *mask)
+static struct task_struct *select_bad_process(unsigned int *ppoints,
+		unsigned long totalpages, struct mem_cgroup *mem,
+		enum oom_constraint constraint, const nodemask_t *mask)
 {
 	struct task_struct *p;
 	struct task_struct *chosen = NULL;
@@ -263,7 +289,7 @@ static struct task_struct *select_bad_process(unsigned long *ppoints,
 
 	do_posix_clock_monotonic_gettime(&uptime);
 	for_each_process(p) {
-		unsigned long points;
+		unsigned int points;
 
 		/*
 		 * skip kernel threads and tasks which have already released
@@ -308,13 +334,13 @@ static struct task_struct *select_bad_process(unsigned long *ppoints,
 				return ERR_PTR(-1UL);
 
 			chosen = p;
-			*ppoints = ULONG_MAX;
+			*ppoints = 1000;
 		}
 
-		if (p->signal->oom_adj == OOM_DISABLE)
+		if (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
 			continue;
 
-		points = badness(p, uptime.tv_sec);
+		points = oom_badness(p, totalpages, uptime.tv_sec);
 		if (points > *ppoints || !chosen) {
 			chosen = p;
 			*ppoints = points;
@@ -330,7 +356,7 @@ static struct task_struct *select_bad_process(unsigned long *ppoints,
  *
  * Dumps the current memory state of all system tasks, excluding kernel threads.
  * State information includes task's pid, uid, tgid, vm size, rss, cpu, oom_adj
- * score, and name.
+ * value, oom_score_adj value, and name.
  *
  * If the actual is non-NULL, only tasks that are a member of the mem_cgroup are
  * shown.
@@ -342,7 +368,7 @@ static void dump_tasks(const struct mem_cgroup *mem)
 	struct task_struct *g, *p;
 
 	printk(KERN_INFO "[ pid ]   uid  tgid total_vm      rss cpu oom_adj "
-	       "name\n");
+	       "oom_score_adj name\n");
 	do_each_thread(g, p) {
 		struct mm_struct *mm;
 
@@ -362,10 +388,10 @@ static void dump_tasks(const struct mem_cgroup *mem)
 			task_unlock(p);
 			continue;
 		}
-		printk(KERN_INFO "[%5d] %5d %5d %8lu %8lu %3d     %3d %s\n",
+		pr_info("[%5d] %5d %5d %8lu %8lu %3d     %3d          %4d %s\n",
 		       p->pid, __task_cred(p)->uid, p->tgid, mm->total_vm,
 		       get_mm_rss(mm), (int)task_cpu(p), p->signal->oom_adj,
-		       p->comm);
+		       p->signal->oom_score_adj, p->comm);
 		task_unlock(p);
 	} while_each_thread(g, p);
 }
@@ -374,8 +400,9 @@ static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
 							struct mem_cgroup *mem)
 {
 	pr_warning("%s invoked oom-killer: gfp_mask=0x%x, order=%d, "
-		"oom_adj=%d\n",
-		current->comm, gfp_mask, order, current->signal->oom_adj);
+		"oom_adj=%d, oom_score_adj=%d\n",
+		current->comm, gfp_mask, order, current->signal->oom_adj,
+		current->signal->oom_score_adj);
 	task_lock(current);
 	cpuset_print_task_mems_allowed(current);
 	task_unlock(current);
@@ -440,7 +467,7 @@ static int oom_kill_task(struct task_struct *p)
 	 * change to NULL at any time since we do not hold task_lock(p).
 	 * However, this is of no concern to us.
 	 */
-	if (!p->mm || p->signal->oom_adj == OOM_DISABLE)
+	if (!p->mm || p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
 		return 1;
 
 	__oom_kill_task(p, 1);
@@ -449,12 +476,12 @@ static int oom_kill_task(struct task_struct *p)
 }
 
 static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
-			    unsigned long points, struct mem_cgroup *mem,
-			    const char *message)
+			    unsigned int points, unsigned long totalpages,
+			    struct mem_cgroup *mem, const char *message)
 {
 	struct task_struct *victim = p;
 	struct task_struct *c;
-	unsigned long victim_points = 0;
+	unsigned int victim_points = 0;
 	struct timespec uptime;
 
 	if (printk_ratelimit())
@@ -469,21 +496,21 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
 		return 0;
 	}
 
-	pr_err("%s: Kill process %d (%s) with score %lu or sacrifice child\n",
+	pr_err("%s: Kill process %d (%s) with score %d or sacrifice child\n",
 		message, task_pid_nr(p), p->comm, points);
 
 	do_posix_clock_monotonic_gettime(&uptime);
 	/* Try to sacrifice the worst child first */
 	list_for_each_entry(c, &p->children, sibling) {
-		unsigned long cpoints;
+		unsigned int cpoints;
 
 		if (c->mm == p->mm)
 			continue;
 		if (mem && !task_in_mem_cgroup(c, mem))
 			continue;
 
-		/* badness() returns 0 if the thread is unkillable */
-		cpoints = badness(c, uptime.tv_sec);
+		/* oom_badness() returns 0 if the thread is unkillable */
+		cpoints = oom_badness(c, totalpages, uptime.tv_sec);
 		if (cpoints > victim_points) {
 			victim = c;
 			victim_points = cpoints;
@@ -495,21 +522,24 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
 #ifdef CONFIG_CGROUP_MEM_RES_CTLR
 void mem_cgroup_out_of_memory(struct mem_cgroup *mem, gfp_t gfp_mask)
 {
-	unsigned long points = 0;
+	unsigned long limit;
+	unsigned int points = 0;
 	struct task_struct *p;
 
 	if (sysctl_panic_on_oom == 2)
 		panic("out of memory(memcg). panic_on_oom is selected.\n");
+
+	limit = mem_cgroup_get_limit(mem) >> PAGE_SHIFT;
 	read_lock(&tasklist_lock);
 retry:
-	p = select_bad_process(&points, mem, CONSTRAINT_NONE, NULL);
+	p = select_bad_process(&points, limit, mem, CONSTRAINT_NONE, NULL);
 	if (PTR_ERR(p) == -1UL)
 		goto out;
 
 	if (!p)
 		p = current;
 
-	if (oom_kill_process(p, gfp_mask, 0, points, mem,
+	if (oom_kill_process(p, gfp_mask, 0, points, limit, mem,
 				"Memory cgroup out of memory"))
 		goto retry;
 out:
@@ -622,22 +652,22 @@ static void clear_system_oom(void)
 /*
  * Must be called with tasklist_lock held for read.
  */
-static void __out_of_memory(gfp_t gfp_mask, int order,
+static void __out_of_memory(gfp_t gfp_mask, int order, unsigned long totalpages,
 			enum oom_constraint constraint, const nodemask_t *mask)
 {
 	struct task_struct *p;
-	unsigned long points;
+	unsigned int points;
 
 	if (sysctl_oom_kill_allocating_task)
-		if (!oom_kill_process(current, gfp_mask, order, 0, NULL,
-				"Out of memory (oom_kill_allocating_task)"))
+		if (!oom_kill_process(current, gfp_mask, order, 0, totalpages,
+			NULL, "Out of memory (oom_kill_allocating_task)"))
 			return;
 retry:
 	/*
 	 * Rambo mode: Shoot down a process and hope it solves whatever
 	 * issues we may have.
 	 */
-	p = select_bad_process(&points, NULL, constraint, mask);
+	p = select_bad_process(&points, totalpages, NULL, constraint, mask);
 
 	if (PTR_ERR(p) == -1UL)
 		return;
@@ -649,7 +679,7 @@ retry:
 		panic("Out of memory and no killable processes...\n");
 	}
 
-	if (oom_kill_process(p, gfp_mask, order, points, NULL,
+	if (oom_kill_process(p, gfp_mask, order, points, totalpages, NULL,
 			     "Out of memory"))
 		goto retry;
 }
@@ -669,6 +699,7 @@ retry:
 void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
 		int order, nodemask_t *nodemask)
 {
+	unsigned long totalpages;
 	unsigned long freed = 0;
 	enum oom_constraint constraint = CONSTRAINT_NONE;
 
@@ -686,8 +717,8 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
 	 * Check if there were limitations on the allocation (only relevant for
 	 * NUMA) that may require different handling.
 	 */
-	if (zonelist)
-		constraint = constrained_alloc(zonelist, gfp_mask, nodemask);
+	constraint = constrained_alloc(zonelist, gfp_mask, nodemask,
+						&totalpages);
 	read_lock(&tasklist_lock);
 	if (unlikely(sysctl_panic_on_oom)) {
 		/*
@@ -701,7 +732,7 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
 			panic("Out of memory: panic_on_oom is enabled\n");
 		}
 	}
-	__out_of_memory(gfp_mask, order, constraint, nodemask);
+	__out_of_memory(gfp_mask, order, totalpages, constraint, nodemask);
 	read_unlock(&tasklist_lock);
 
 	/*

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Re: [patch 05/10 -mm v3] oom: badness heuristic rewrite

[KAMEZAWA Hiroyuki]

On Wed, 10 Mar 2010 02:41:32 -0800 (PST)
David Rientjes <rientjes@google.com> wrote:

>  	if (sysctl_panic_on_oom == 2)
>  		panic("out of memory(memcg). panic_on_oom is selected.\n");
> +
> +	limit = mem_cgroup_get_limit(mem) >> PAGE_SHIFT;

A small concern here.

+u64 mem_cgroup_get_limit(struct mem_cgroup *memcg)
+{
+       return res_counter_read_u64(&memcg->memsw, RES_LIMIT);
+}

Because memory cgroup has 2 limit controls as "memory" and "memory+swap",
a user may set only "memory" limitation. (Especially on swapless system.)
Then, memcg->memsw limit can be infinite in some situation.

So, how about this ? (just an idea after breif thinking..)

u64 mem_cgroup_get_memsw_limit(struct mem_cgroup *memcg)
{
	u64 memlimit, memswlimit;

	memlimit = res_counter_read_u64(&memcg->res, RES_LIMIT);
	memswlimit = res_counter_read_u64(&memcg->memsw, RES_LIMIT);
	if (memlimit + total_swap_pages > memswlimit)
		return memswlimit;
	return memlimit + total_swap_pages;
}

Thanks,
-Kame

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Re: [patch 05/10 -mm v3] oom: badness heuristic rewrite

[David Rientjes]

On Fri, 12 Mar 2010, KAMEZAWA Hiroyuki wrote:

> A small concern here.
> 
> +u64 mem_cgroup_get_limit(struct mem_cgroup *memcg)
> +{
> +       return res_counter_read_u64(&memcg->memsw, RES_LIMIT);
> +}
> 
> Because memory cgroup has 2 limit controls as "memory" and "memory+swap",
> a user may set only "memory" limitation. (Especially on swapless system.)
> Then, memcg->memsw limit can be infinite in some situation.
> 
> So, how about this ? (just an idea after breif thinking..)
> 
> u64 mem_cgroup_get_memsw_limit(struct mem_cgroup *memcg)
> {
> 	u64 memlimit, memswlimit;
> 
> 	memlimit = res_counter_read_u64(&memcg->res, RES_LIMIT);
> 	memswlimit = res_counter_read_u64(&memcg->memsw, RES_LIMIT);
> 	if (memlimit + total_swap_pages > memswlimit)
> 		return memswlimit;
> 	return memlimit + total_swap_pages;
> }
> 

I definitely trust your judgment when it comes to memcg, so this is how I 
implemented it for v4.

Is the memcg->memsw RES_LIMIT not initialized to zero for swapless systems 
or when users don't set a value?  In other words, is this the optimal way 
to determine how much resident memory and swap that current's memcg is 
allowed?

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Re: [patch 05/10 -mm v3] oom: badness heuristic rewrite

[KAMEZAWA Hiroyuki]

On Tue, 16 Mar 2010 18:26:30 -0700 (PDT)
David Rientjes <rientjes@google.com> wrote:

> On Fri, 12 Mar 2010, KAMEZAWA Hiroyuki wrote:
> 
> > A small concern here.
> > 
> > +u64 mem_cgroup_get_limit(struct mem_cgroup *memcg)
> > +{
> > +       return res_counter_read_u64(&memcg->memsw, RES_LIMIT);
> > +}
> > 
> > Because memory cgroup has 2 limit controls as "memory" and "memory+swap",
> > a user may set only "memory" limitation. (Especially on swapless system.)
> > Then, memcg->memsw limit can be infinite in some situation.
> > 
> > So, how about this ? (just an idea after breif thinking..)
> > 
> > u64 mem_cgroup_get_memsw_limit(struct mem_cgroup *memcg)
> > {
> > 	u64 memlimit, memswlimit;
> > 
> > 	memlimit = res_counter_read_u64(&memcg->res, RES_LIMIT);
> > 	memswlimit = res_counter_read_u64(&memcg->memsw, RES_LIMIT);
> > 	if (memlimit + total_swap_pages > memswlimit)
> > 		return memswlimit;
> > 	return memlimit + total_swap_pages;
> > }
> > 
> 
> I definitely trust your judgment when it comes to memcg, so this is how I 
> implemented it for v4.
> 
> Is the memcg->memsw RES_LIMIT not initialized to zero for swapless systems 
> or when users don't set a value?  
It's initalized to inifinite (-1UL).

> In other words, is this the optimal way 
> to determine how much resident memory and swap that current's memcg is 
> allowed?
> 
I think so.

It's guaranteed that
	mem->res.limit <= mem->memsw.limit

Then, only when
	mem->res.limit + total_swap_pages > mem->memsw.limit
memsw.limit works.

Thanks,
-Kame







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Re: [patch 05/10 -mm v3] oom: badness heuristic rewrite

[David Rientjes]

On Wed, 17 Mar 2010, KAMEZAWA Hiroyuki wrote:

> > > u64 mem_cgroup_get_memsw_limit(struct mem_cgroup *memcg)
> > > {
> > > 	u64 memlimit, memswlimit;
> > > 
> > > 	memlimit = res_counter_read_u64(&memcg->res, RES_LIMIT);
> > > 	memswlimit = res_counter_read_u64(&memcg->memsw, RES_LIMIT);
> > > 	if (memlimit + total_swap_pages > memswlimit)
> > > 		return memswlimit;
> > > 	return memlimit + total_swap_pages;
> > > }
> > > 
> > 
> > I definitely trust your judgment when it comes to memcg, so this is how I 
> > implemented it for v4.
> > 
> > Is the memcg->memsw RES_LIMIT not initialized to zero for swapless systems 
> > or when users don't set a value?  
> It's initalized to inifinite (-1UL).
> 

Ah, that makes sense.

> > In other words, is this the optimal way 
> > to determine how much resident memory and swap that current's memcg is 
> > allowed?
> > 
> I think so.
> 
> It's guaranteed that
> 	mem->res.limit <= mem->memsw.limit
> 
> Then, only when
> 	mem->res.limit + total_swap_pages > mem->memsw.limit
> memsw.limit works.
> 

Ok, I'll use your suggestion and then it can be maintained in 
mm/memcontrol.c for any future updates.

Thanks.

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[patch 06/10 -mm v3] oom: deprecate oom_adj tunable

[David Rientjes]

/proc/pid/oom_adj is now deprecated so that that it may eventually be
removed.  The target date for removal is December 2011.

A warning will be printed to the kernel log if a task attempts to use
this interface.  Future warning will be suppressed until the kernel is
rebooted to prevent spamming the kernel log.

Signed-off-by: David Rientjes <rientjes@google.com>
---
 Documentation/feature-removal-schedule.txt |   30 ++++++++++++++++++++++++++++
 Documentation/filesystems/proc.txt         |    3 ++
 fs/proc/base.c                             |    8 +++++++
 include/linux/oom.h                        |    3 ++
 4 files changed, 44 insertions(+), 0 deletions(-)

diff --git a/Documentation/feature-removal-schedule.txt b/Documentation/feature-removal-schedule.txt
--- a/Documentation/feature-removal-schedule.txt
+++ b/Documentation/feature-removal-schedule.txt
@@ -174,6 +174,36 @@ Who:	Eric Biederman <ebiederm@xmission.com>
 
 ---------------------------
 
+What:	/proc/<pid>/oom_adj
+When:	December 2011
+Why:	/proc/<pid>/oom_adj allows userspace to influence the oom killer's
+	badness heuristic used to determine which task to kill when the kernel
+	is out of memory.
+
+	The badness heuristic has since been rewritten since the introduction of
+	this tunable such that its meaning is deprecated.  The value was
+	implemented as a bitshift on a score generated by the badness()
+	function that did not have any precise units of measure.  With the
+	rewrite, the score is given as a proportion of available memory to the
+	task allocating pages, so using a bitshift which grows the score
+	exponentially is, thus, impossible to tune with fine granularity.
+
+	A much more powerful interface, /proc/<pid>/oom_score_adj, was
+	introduced with the oom killer rewrite that allows users to increase or
+	decrease the badness() score linearly.  This interface will replace
+	/proc/<pid>/oom_adj.
+
+	See Documentation/filesystems/proc.txt for information on how to use the
+	new tunable.
+
+	A warning will be emitted to the kernel log if an application uses this
+	deprecated interface.  After it is printed once, future warning will be
+	suppressed until the kernel is rebooted.
+
+Who:	David Rientjes <rientjes@google.com>
+
+---------------------------
+
 What:	remove EXPORT_SYMBOL(kernel_thread)
 When:	August 2006
 Files:	arch/*/kernel/*_ksyms.c
diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -1290,6 +1290,9 @@ scaled linearly with /proc/<pid>/oom_score_adj.
 Writing to /proc/<pid>/oom_score_adj or /proc/<pid>/oom_adj will change the
 other with its scaled value.
 
+NOTICE: /proc/<pid>/oom_adj is deprecated and will be removed, please see
+Documentation/feature-removal-schedule.txt.
+
 Caveat: when a parent task is selected, the oom killer will sacrifice any first
 generation children with seperate address spaces instead, if possible.  This
 avoids servers and important system daemons from being killed and loses the
diff --git a/fs/proc/base.c b/fs/proc/base.c
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1138,6 +1138,14 @@ static ssize_t oom_adjust_write(struct file *file, const char __user *buf,
 		return -EACCES;
 	}
 
+	/*
+	 * Warn that /proc/pid/oom_adj is deprecated, see
+	 * Documentation/feature-removal-schedule.txt.
+	 */
+	printk_once(KERN_WARNING "%s (%d): /proc/%d/oom_adj is deprecated, "
+			"please use /proc/%d/oom_score_adj instead.\n",
+			current->comm, task_pid_nr(current),
+			task_pid_nr(task), task_pid_nr(task));
 	task->signal->oom_adj = oom_adjust;
 	/*
 	 * Scale /proc/pid/oom_score_adj appropriately ensuring that a maximum
diff --git a/include/linux/oom.h b/include/linux/oom.h
--- a/include/linux/oom.h
+++ b/include/linux/oom.h
@@ -2,6 +2,9 @@
 #define __INCLUDE_LINUX_OOM_H
 
 /*
+ * /proc/<pid>/oom_adj is deprecated, see
+ * Documentation/feature-removal-schedule.txt.
+ *
  * /proc/<pid>/oom_adj set to -17 protects from the oom-killer
  */
 #define OOM_DISABLE (-17)

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[patch 07/10 -mm v3] oom: replace sysctls with quick mode

[David Rientjes]

Two VM sysctls, oom dump_tasks and oom_kill_allocating_task, were
implemented for very large systems to avoid excessively long tasklist
scans.  The former suppresses helpful diagnostic messages that are
emitted for each thread group leader that are candidates for oom kill
including their pid, uid, vm size, rss, oom_adj value, and name; this
information is very helpful to users in understanding why a particular
task was chosen for kill over others.  The latter simply kills current,
the task triggering the oom condition, instead of iterating through the
tasklist looking for the worst offender.

Both of these sysctls are combined into one for use on the aforementioned
large systems: oom_kill_quick.  This disables the now-default
oom_dump_tasks and kills current whenever the oom killer is called.

This consolidation is possible because the audience for both tunables is
the same and there is no backwards compatibility issue in removing
oom_dump_tasks since its behavior is now default.  Since mempolicy ooms
now scan the tasklist, oom_kill_allocating_task may now find more users
to avoid the performance penalty, so it's better to unite them under one
sysctl than carry two for legacy purposes.

Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: David Rientjes <rientjes@google.com>
---
 Documentation/sysctl/vm.txt |   44 +++++-------------------------------------
 include/linux/oom.h         |    3 +-
 kernel/sysctl.c             |   13 ++---------
 mm/oom_kill.c               |    9 +++----
 4 files changed, 14 insertions(+), 55 deletions(-)

diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
--- a/Documentation/sysctl/vm.txt
+++ b/Documentation/sysctl/vm.txt
@@ -43,9 +43,8 @@ Currently, these files are in /proc/sys/vm:
 - nr_pdflush_threads
 - nr_trim_pages         (only if CONFIG_MMU=n)
 - numa_zonelist_order
-- oom_dump_tasks
 - oom_forkbomb_thres
-- oom_kill_allocating_task
+- oom_kill_quick
 - overcommit_memory
 - overcommit_ratio
 - page-cluster
@@ -470,27 +469,6 @@ this is causing problems for your system/application.
 
 ==============================================================
 
-oom_dump_tasks
-
-Enables a system-wide task dump (excluding kernel threads) to be
-produced when the kernel performs an OOM-killing and includes such
-information as pid, uid, tgid, vm size, rss, cpu, oom_adj score, and
-name.  This is helpful to determine why the OOM killer was invoked
-and to identify the rogue task that caused it.
-
-If this is set to zero, this information is suppressed.  On very
-large systems with thousands of tasks it may not be feasible to dump
-the memory state information for each one.  Such systems should not
-be forced to incur a performance penalty in OOM conditions when the
-information may not be desired.
-
-If this is set to non-zero, this information is shown whenever the
-OOM killer actually kills a memory-hogging task.
-
-The default value is 0.
-
-==============================================================
-
 oom_forkbomb_thres
 
 This value defines how many children with a seperate address space a specific
@@ -511,22 +489,12 @@ The default value is 1000.
 
 ==============================================================
 
-oom_kill_allocating_task
-
-This enables or disables killing the OOM-triggering task in
-out-of-memory situations.
-
-If this is set to zero, the OOM killer will scan through the entire
-tasklist and select a task based on heuristics to kill.  This normally
-selects a rogue memory-hogging task that frees up a large amount of
-memory when killed.
-
-If this is set to non-zero, the OOM killer simply kills the task that
-triggered the out-of-memory condition.  This avoids the expensive
-tasklist scan.
+oom_kill_quick
 
-If panic_on_oom is selected, it takes precedence over whatever value
-is used in oom_kill_allocating_task.
+When enabled, this will always kill the task that triggered the oom killer, i.e.
+the task that attempted to allocate memory that could not be found.  It also
+suppresses the tasklist dump to the kernel log whenever the oom killer is
+called.  Typically set on systems with an extremely large number of tasks.
 
 The default value is 0.
 
diff --git a/include/linux/oom.h b/include/linux/oom.h
--- a/include/linux/oom.h
+++ b/include/linux/oom.h
@@ -63,8 +63,7 @@ static inline void oom_killer_enable(void)
 }
 /* for sysctl */
 extern int sysctl_panic_on_oom;
-extern int sysctl_oom_kill_allocating_task;
-extern int sysctl_oom_dump_tasks;
+extern int sysctl_oom_kill_quick;
 extern int sysctl_oom_forkbomb_thres;
 
 #endif /* __KERNEL__*/
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -940,16 +940,9 @@ static struct ctl_table vm_table[] = {
 		.proc_handler	= proc_dointvec,
 	},
 	{
-		.procname	= "oom_kill_allocating_task",
-		.data		= &sysctl_oom_kill_allocating_task,
-		.maxlen		= sizeof(sysctl_oom_kill_allocating_task),
-		.mode		= 0644,
-		.proc_handler	= proc_dointvec,
-	},
-	{
-		.procname	= "oom_dump_tasks",
-		.data		= &sysctl_oom_dump_tasks,
-		.maxlen		= sizeof(sysctl_oom_dump_tasks),
+		.procname	= "oom_kill_quick",
+		.data		= &sysctl_oom_kill_quick,
+		.maxlen		= sizeof(sysctl_oom_kill_quick),
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec,
 	},
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -32,9 +32,8 @@
 #include <linux/security.h>
 
 int sysctl_panic_on_oom;
-int sysctl_oom_kill_allocating_task;
-int sysctl_oom_dump_tasks;
 int sysctl_oom_forkbomb_thres = DEFAULT_OOM_FORKBOMB_THRES;
+int sysctl_oom_kill_quick;
 static DEFINE_SPINLOCK(zone_scan_lock);
 
 /*
@@ -409,7 +408,7 @@ static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
 	dump_stack();
 	mem_cgroup_print_oom_info(mem, p);
 	show_mem();
-	if (sysctl_oom_dump_tasks)
+	if (!sysctl_oom_kill_quick)
 		dump_tasks(mem);
 }
 
@@ -658,9 +657,9 @@ static void __out_of_memory(gfp_t gfp_mask, int order, unsigned long totalpages,
 	struct task_struct *p;
 	unsigned int points;
 
-	if (sysctl_oom_kill_allocating_task)
+	if (sysctl_oom_kill_quick)
 		if (!oom_kill_process(current, gfp_mask, order, 0, totalpages,
-			NULL, "Out of memory (oom_kill_allocating_task)"))
+			NULL, "Out of memory (quick mode)"))
 			return;
 retry:
 	/*

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[patch 08/10 -mm v3] oom: avoid oom killer for lowmem allocations

[David Rientjes]

If memory has been depleted in lowmem zones even with the protection
afforded to it by /proc/sys/vm/lowmem_reserve_ratio, it is unlikely that
killing current users will help.  The memory is either reclaimable (or
migratable) already, in which case we should not invoke the oom killer at
all, or it is pinned by an application for I/O.  Killing such an
application may leave the hardware in an unspecified state and there is
no guarantee that it will be able to make a timely exit.

Lowmem allocations are now failed in oom conditions when __GFP_NOFAIL is
not used so that the task can perhaps recover or try again later.

Previously, the heuristic provided some protection for those tasks with 
CAP_SYS_RAWIO, but this is no longer necessary since we will not be
killing tasks for the purposes of ISA allocations.

high_zoneidx is gfp_zone(gfp_flags), meaning that ZONE_NORMAL will be the
default for all allocations that are not __GFP_DMA, __GFP_DMA32,
__GFP_HIGHMEM, and __GFP_MOVABLE on kernels configured to support those
flags.  Testing for high_zoneidx being less than ZONE_NORMAL will only
return true for allocations that have either __GFP_DMA or __GFP_DMA32.

Signed-off-by: David Rientjes <rientjes@google.com>
---
 mm/page_alloc.c |   29 ++++++++++++++++++++---------
 1 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1695,6 +1695,9 @@ __alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order,
 		/* The OOM killer will not help higher order allocs */
 		if (order > PAGE_ALLOC_COSTLY_ORDER)
 			goto out;
+		/* The OOM killer does not needlessly kill tasks for lowmem */
+		if (high_zoneidx < ZONE_NORMAL)
+			goto out;
 		/*
 		 * GFP_THISNODE contains __GFP_NORETRY and we never hit this.
 		 * Sanity check for bare calls of __GFP_THISNODE, not real OOM.
@@ -1923,15 +1926,23 @@ rebalance:
 			if (page)
 				goto got_pg;
 
-			/*
-			 * The OOM killer does not trigger for high-order
-			 * ~__GFP_NOFAIL allocations so if no progress is being
-			 * made, there are no other options and retrying is
-			 * unlikely to help.
-			 */
-			if (order > PAGE_ALLOC_COSTLY_ORDER &&
-						!(gfp_mask & __GFP_NOFAIL))
-				goto nopage;
+			if (!(gfp_mask & __GFP_NOFAIL)) {
+				/*
+				 * The oom killer is not called for high-order
+				 * allocations that may fail, so if no progress
+				 * is being made, there are no other options and
+				 * retrying is unlikely to help.
+				 */
+				if (order > PAGE_ALLOC_COSTLY_ORDER)
+					goto nopage;
+				/*
+				 * The oom killer is not called for lowmem
+				 * allocations to prevent needlessly killing
+				 * innocent tasks.
+				 */
+				if (high_zoneidx < ZONE_NORMAL)
+					goto nopage;
+			}
 
 			goto restart;
 		}

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[patch 09/10 -mm v3] oom: remove unnecessary code and cleanup

[David Rientjes]

Remove the redundancy in __oom_kill_task() since:

 - init can never be passed to this function: it will never be PF_EXITING
   or selectable from select_bad_process(), and

 - it will never be passed a task from oom_kill_task() without an ->mm
   and we're unconcerned about detachment from exiting tasks, there's no
   reason to protect them against SIGKILL or access to memory reserves.

Also moves the kernel log message to a higher level since the verbosity
is not always emitted here; we need not print an error message if an
exiting task is given a longer timeslice.

Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: David Rientjes <rientjes@google.com>
---
 mm/oom_kill.c |   64 ++++++++++++++------------------------------------------
 1 files changed, 16 insertions(+), 48 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -412,67 +412,35 @@ static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order,
 		dump_tasks(mem);
 }
 
-#define K(x) ((x) << (PAGE_SHIFT-10))
-
 /*
- * Send SIGKILL to the selected  process irrespective of  CAP_SYS_RAW_IO
- * flag though it's unlikely that  we select a process with CAP_SYS_RAW_IO
- * set.
+ * Give the oom killed task high priority and access to memory reserves so that
+ * it may quickly exit and free its memory.
  */
-static void __oom_kill_task(struct task_struct *p, int verbose)
+static void __oom_kill_task(struct task_struct *p)
 {
-	if (is_global_init(p)) {
-		WARN_ON(1);
-		printk(KERN_WARNING "tried to kill init!\n");
-		return;
-	}
-
-	task_lock(p);
-	if (!p->mm) {
-		WARN_ON(1);
-		printk(KERN_WARNING "tried to kill an mm-less task %d (%s)!\n",
-			task_pid_nr(p), p->comm);
-		task_unlock(p);
-		return;
-	}
-
-	if (verbose)
-		printk(KERN_ERR "Killed process %d (%s) "
-		       "vsz:%lukB, anon-rss:%lukB, file-rss:%lukB\n",
-		       task_pid_nr(p), p->comm,
-		       K(p->mm->total_vm),
-		       K(get_mm_counter(p->mm, MM_ANONPAGES)),
-		       K(get_mm_counter(p->mm, MM_FILEPAGES)));
-	task_unlock(p);
-
-	/*
-	 * We give our sacrificial lamb high priority and access to
-	 * all the memory it needs. That way it should be able to
-	 * exit() and clear out its resources quickly...
-	 */
 	p->rt.time_slice = HZ;
 	set_tsk_thread_flag(p, TIF_MEMDIE);
-
 	force_sig(SIGKILL, p);
 }
 
+#define K(x) ((x) << (PAGE_SHIFT-10))
 static int oom_kill_task(struct task_struct *p)
 {
-	/* WARNING: mm may not be dereferenced since we did not obtain its
-	 * value from get_task_mm(p).  This is OK since all we need to do is
-	 * compare mm to q->mm below.
-	 *
-	 * Furthermore, even if mm contains a non-NULL value, p->mm may
-	 * change to NULL at any time since we do not hold task_lock(p).
-	 * However, this is of no concern to us.
-	 */
-	if (!p->mm || p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
+	task_lock(p);
+	if (!p->mm || p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN) {
+		task_unlock(p);
 		return 1;
+	}
+	pr_err("Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB\n",
+		task_pid_nr(p), p->comm, K(p->mm->total_vm),
+	       K(get_mm_counter(p->mm, MM_ANONPAGES)),
+	       K(get_mm_counter(p->mm, MM_FILEPAGES)));
+	task_unlock(p);
 
-	__oom_kill_task(p, 1);
-
+	__oom_kill_task(p);
 	return 0;
 }
+#undef K
 
 static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
 			    unsigned int points, unsigned long totalpages,
@@ -491,7 +459,7 @@ static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
 	 * its children or threads, just set TIF_MEMDIE so it can die quickly
 	 */
 	if (p->flags & PF_EXITING) {
-		__oom_kill_task(p, 0);
+		__oom_kill_task(p);
 		return 0;
 	}
 

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[patch 10/10 -mm v3] oom: default to killing current for pagefault ooms

[David Rientjes]

The pagefault oom handler does not know the context (gfp_mask, order,
etc) in which memory was not found when a VM_FAULT_OOM is generated.  The
only information known is that current is trying to allocate in that
context, so killing it is a legitimate response (and is the default for
architectures that do not even use the pagefault oom handler such as ia64
and powerpc).

When a VM_FAULT_OOM occurs, the pagefault oom handler will now attempt to
kill current by default.  If it is unkillable, the oom killer is called
to find a memory-hogging task to kill instead that will lead to future
memory freeing.

Signed-off-by: David Rientjes <rientjes@google.com>
---
 mm/oom_kill.c |   18 +++++++++++++-----
 1 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -711,15 +711,23 @@ void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask,
 }
 
 /*
- * The pagefault handler calls here because it is out of memory, so kill a
- * memory-hogging task.  If a populated zone has ZONE_OOM_LOCKED set, a parallel
- * oom killing is already in progress so do nothing.  If a task is found with
- * TIF_MEMDIE set, it has been killed so do nothing and allow it to exit.
+ * The pagefault handler calls here because it is out of memory, so kill current
+ * by default.  If it's unkillable, then fallback to killing a memory-hogging
+ * task.  If a populated zone has ZONE_OOM_LOCKED set, a parallel oom killing is
+ * already in progress so do nothing.  If a task is found with TIF_MEMDIE set,
+ * it has been killed so do nothing and allow it to exit.
  */
 void pagefault_out_of_memory(void)
 {
+	unsigned long totalpages;
+	int err;
+
 	if (try_set_system_oom()) {
-		out_of_memory(NULL, 0, 0, NULL);
+		constrained_alloc(NULL, 0, NULL, &totalpages);
+		err = oom_kill_process(current, 0, 0, 0, totalpages, NULL,
+					"Out of memory (pagefault)");
+		if (err)
+			out_of_memory(NULL, 0, 0, NULL);
 		clear_system_oom();
 	}
 	if (!test_thread_flag(TIF_MEMDIE))

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Re: [patch 00/10 -mm v3] oom killer rewrite

[KAMEZAWA Hiroyuki]

On Wed, 10 Mar 2010 02:41:08 -0800 (PST)
David Rientjes <rientjes@google.com> wrote:

> This patchset is a rewrite of the out of memory killer to address several
> issues that have been raised recently.  The most notable change is a
> complete rewrite of the badness heuristic that determines which task is
> killed; the goal was to make it as simple and predictable as possible
> while still addressing issues that plague the VM.
> 
> Changes from version 2:
> 
>  - updated to mmotm-2010-03-09-19-15
> 
>  - schedule a timeout for current if it was not selected for oom kill
>    when it has returned VM_FAULT_OOM so memory can freed to prevent
>    needlessly recalling the oom killer and looping.
> 

To me, this seems to work nicer than current oom-killer, memory eater dies 1st. 
thanks.

BTW, it seems there are still chances for serial-oom-killer.

Assume I run memory eater (called malloc) on a host.
==
Mar 13 13:05:56 localhost kernel: malloc invoked oom-killer: gfp_mask=0x280da, order=0, oom_adj=0, oom_score_adj=0
Mar 13 13:05:56 localhost kernel: malloc cpuset=/ mems_allowed=0
Mar 13 13:05:56 localhost kernel: Pid: 2525, comm: malloc Not tainted 2.6.34-rc1-mm1+ #3
Mar 13 13:05:56 localhost kernel: Call Trace:
Mar 13 13:05:56 localhost kernel: [<ffffffff8108aebf>] ? cpuset_print_task_mems_allowed+0x91/0x9c
Mar 13 13:05:56 localhost kernel: [<ffffffff810c90c1>] dump_header+0x74/0x1af
<snip>
Mar 13 13:05:56 localhost kernel: [ 2525]   500  2525   434340   433346   0       0             0 malloc
Mar 13 13:05:56 localhost kernel: Out of memory: Kill process 2525 (malloc) with score 967 or sacrifice child
Mar 13 13:05:56 localhost kernel: Killed process 2525 (malloc) total-vm:1737360kB, anon-rss:1733364kB, file-rss:20kB
Mar 13 13:05:56 localhost kernel: rsyslogd invoked oom-killer: gfp_mask=0x201da, order=0, oom_adj=0, oom_score_adj=0
Mar 13 13:05:56 localhost kernel: rsyslogd cpuset=/ mems_allowed=0
Mar 13 13:05:56 localhost kernel: Pid: 696, comm: rsyslogd Not tainted 2.6.34-rc1-mm1+ #3
Mar 13 13:05:56 localhost kernel: Call Trace:
Mar 13 13:05:56 localhost kernel: [<ffffffff8108aebf>] ? cpuset_print_task_mems_allowed+0x91/0x9c
Mar 13 13:05:56 localhost kernel: [<ffffffff810c90c1>] dump_header+0x74/0x1af
Mar 13 13:05:56 localhost kernel: [<ffffffff81211a8e>] ? ___ratelimit+0xe6/0x104
Mar 13 13:05:56 localhost kernel: [<ffffffff810c942a>] oom_kill_process+0x49/0x1ed
<snip>
Mar 13 13:05:56 localhost kernel: 480 total pagecache pages
Mar 13 13:05:56 localhost kernel: 0 pages in swap cache
Mar 13 13:05:56 localhost kernel: Swap cache stats: add 0, delete 0, find 0/0
Mar 13 13:05:56 localhost kernel: Free swap  = 0kB
Mar 13 13:05:56 localhost kernel: Total swap = 0kB
Mar 13 13:05:56 localhost kernel: 2097151 pages RAM
Mar 13 13:05:56 localhost kernel: 48776 pages reserved
Mar 13 13:05:56 localhost kernel: 1356 pages shared
Mar 13 13:05:56 localhost kernel: 458132 pages non-shared
<snip>
Mar 13 13:05:56 localhost kernel: [ 2506]     0  2506     3120       55   0       0             0 anacron
Mar 13 13:05:56 localhost kernel: Out of memory: Kill process 1267 (gdm-simple-gree) with score 2 or sacrifice child
Mar 13 13:05:56 localhost kernel: Killed process 1267 (gdm-simple-gree) total-vm:359156kB, anon-rss:4012kB, file-rss:472kB
==

Then, at first, malloc, a bad program is killed. But, another oom-kill happens immediately and 
gdm-simple-gree is killed.

I think there is a task as !p->mm but TIF_MEMDIE task in tasklist.

Because exit_mm()'s logic is as following.
	mm = task->mm
	task->mm = NULL;
	mmput(mm)
		-> free pages under this mm.

This patch make the result better on my box, no serial killer, at least.

-Kame
==

---
 mm/oom_kill.c |   22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

Index: mmotm-2.6.34-Mar11/mm/oom_kill.c
===================================================================
--- mmotm-2.6.34-Mar11.orig/mm/oom_kill.c
+++ mmotm-2.6.34-Mar11/mm/oom_kill.c
@@ -290,6 +290,17 @@ static struct task_struct *select_bad_pr
 	for_each_process(p) {
 		unsigned int points;
 		/*
+		 * This task already has access to memory reserves and is
+		 * being killed. Don't allow any other task access to the
+		 * memory reserve.
+		 *
+		 * Note: this may have a chance of deadlock if it gets
+		 * blocked waiting for another task which itself is waiting
+		 * for memory. Is there a better alternative?
+		 */
+		if (test_tsk_thread_flag(p, TIF_MEMDIE))
+			return ERR_PTR(-1UL);
+		/*
 		 * skip kernel threads and tasks which have already released
 		 * their mm.
 		 */
@@ -305,17 +316,6 @@ static struct task_struct *select_bad_pr
 									 NULL))
 			continue;
 
-		/*
-		 * This task already has access to memory reserves and is
-		 * being killed. Don't allow any other task access to the
-		 * memory reserve.
-		 *
-		 * Note: this may have a chance of deadlock if it gets
-		 * blocked waiting for another task which itself is waiting
-		 * for memory. Is there a better alternative?
-		 */
-		if (test_tsk_thread_flag(p, TIF_MEMDIE))
-			return ERR_PTR(-1UL);
 
 		/*
 		 * This is in the process of releasing memory so wait for it


Thanks,
-Kame


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Re: [patch 00/10 -mm v3] oom killer rewrite

[David Rientjes]

On Fri, 12 Mar 2010, KAMEZAWA Hiroyuki wrote:

> BTW, it seems there are still chances for serial-oom-killer.
> 
> Assume I run memory eater (called malloc) on a host.
> ==
> Mar 13 13:05:56 localhost kernel: malloc invoked oom-killer: gfp_mask=0x280da, order=0, oom_adj=0, oom_score_adj=0
> Mar 13 13:05:56 localhost kernel: malloc cpuset=/ mems_allowed=0
> Mar 13 13:05:56 localhost kernel: Pid: 2525, comm: malloc Not tainted 2.6.34-rc1-mm1+ #3
> Mar 13 13:05:56 localhost kernel: Call Trace:
> Mar 13 13:05:56 localhost kernel: [<ffffffff8108aebf>] ? cpuset_print_task_mems_allowed+0x91/0x9c
> Mar 13 13:05:56 localhost kernel: [<ffffffff810c90c1>] dump_header+0x74/0x1af
> <snip>
> Mar 13 13:05:56 localhost kernel: [ 2525]   500  2525   434340   433346   0       0             0 malloc
> Mar 13 13:05:56 localhost kernel: Out of memory: Kill process 2525 (malloc) with score 967 or sacrifice child
> Mar 13 13:05:56 localhost kernel: Killed process 2525 (malloc) total-vm:1737360kB, anon-rss:1733364kB, file-rss:20kB
> Mar 13 13:05:56 localhost kernel: rsyslogd invoked oom-killer: gfp_mask=0x201da, order=0, oom_adj=0, oom_score_adj=0
> Mar 13 13:05:56 localhost kernel: rsyslogd cpuset=/ mems_allowed=0
> Mar 13 13:05:56 localhost kernel: Pid: 696, comm: rsyslogd Not tainted 2.6.34-rc1-mm1+ #3
> Mar 13 13:05:56 localhost kernel: Call Trace:
> Mar 13 13:05:56 localhost kernel: [<ffffffff8108aebf>] ? cpuset_print_task_mems_allowed+0x91/0x9c
> Mar 13 13:05:56 localhost kernel: [<ffffffff810c90c1>] dump_header+0x74/0x1af
> Mar 13 13:05:56 localhost kernel: [<ffffffff81211a8e>] ? ___ratelimit+0xe6/0x104
> Mar 13 13:05:56 localhost kernel: [<ffffffff810c942a>] oom_kill_process+0x49/0x1ed
> <snip>
> Mar 13 13:05:56 localhost kernel: 480 total pagecache pages
> Mar 13 13:05:56 localhost kernel: 0 pages in swap cache
> Mar 13 13:05:56 localhost kernel: Swap cache stats: add 0, delete 0, find 0/0
> Mar 13 13:05:56 localhost kernel: Free swap  = 0kB
> Mar 13 13:05:56 localhost kernel: Total swap = 0kB
> Mar 13 13:05:56 localhost kernel: 2097151 pages RAM
> Mar 13 13:05:56 localhost kernel: 48776 pages reserved
> Mar 13 13:05:56 localhost kernel: 1356 pages shared
> Mar 13 13:05:56 localhost kernel: 458132 pages non-shared
> <snip>
> Mar 13 13:05:56 localhost kernel: [ 2506]     0  2506     3120       55   0       0             0 anacron
> Mar 13 13:05:56 localhost kernel: Out of memory: Kill process 1267 (gdm-simple-gree) with score 2 or sacrifice child
> Mar 13 13:05:56 localhost kernel: Killed process 1267 (gdm-simple-gree) total-vm:359156kB, anon-rss:4012kB, file-rss:472kB
> ==
> 
> Then, at first, malloc, a bad program is killed. But, another oom-kill happens immediately and 
> gdm-simple-gree is killed.
> 
> I think there is a task as !p->mm but TIF_MEMDIE task in tasklist.
> 

Perhaps, but we should probably handle exit racing conditions with 
PF_EXITING instead of TIF_MEMDIE.  We also need to filter these tasks 
according to memcg and cpusets since oom killed tasks in other cgroups 
shouldn't make the oom killer a no-op for current.

I'll add this:
---
 mm/oom_kill.c |   12 ++++++------
 1 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -290,12 +290,6 @@ static struct task_struct *select_bad_process(unsigned int *ppoints,
 	for_each_process(p) {
 		unsigned int points;
 
-		/*
-		 * skip kernel threads and tasks which have already released
-		 * their mm.
-		 */
-		if (!p->mm)
-			continue;
 		/* skip the init task */
 		if (is_global_init(p))
 			continue;
@@ -336,6 +330,12 @@ static struct task_struct *select_bad_process(unsigned int *ppoints,
 			*ppoints = 1000;
 		}
 
+		/*
+		 * skip kernel threads and tasks which have already released
+		 * their mm.
+		 */
+		if (!p->mm)
+			continue;
 		if (p->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
 			continue;
 

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Re: [patch 00/10 -mm v3] oom killer rewrite

[KAMEZAWA Hiroyuki]

On Wed, 10 Mar 2010 02:41:08 -0800 (PST)
David Rientjes <rientjes@google.com> wrote:

> This patchset is a rewrite of the out of memory killer to address several
> issues that have been raised recently.  The most notable change is a
> complete rewrite of the badness heuristic that determines which task is
> killed; the goal was to make it as simple and predictable as possible
> while still addressing issues that plague the VM.
> 
> Changes from version 2:
> 
>  - updated to mmotm-2010-03-09-19-15
> 
>  - schedule a timeout for current if it was not selected for oom kill
>    when it has returned VM_FAULT_OOM so memory can freed to prevent
>    needlessly recalling the oom killer and looping.
> 
> To apply, download the -mm tree from
> http://userweb.kernel.org/~akpm/mmotm/broken-out.tar.gz first.
> 
> This patchset is also available for each kernel release from:
> 
> 	http://www.kernel.org/pub/linux/kernel/people/rientjes/oom-killer-rewrite/
> 

One question. Assume a host A and B. A has 4G memory, B has 8G memory.

Here, an applicaton which consumes 2G memory.

Then, this application's oom_score will be 500 on A, 250 on B.

How admin detemine the best oom_score_adj value ? Does it depend on envrionment
even if runnning the same application ?

Is it bad to use bare value as

	echo 1G > /proc/<pid>/oom_score_adj

for getting 1G bytes of excuse to this application ?

Thanks,
-Kame














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Re: [patch 00/10 -mm v3] oom killer rewrite

[David Rientjes]

On Fri, 12 Mar 2010, KAMEZAWA Hiroyuki wrote:

> One question. Assume a host A and B. A has 4G memory, B has 8G memory.
> 
> Here, an applicaton which consumes 2G memory.
> 
> Then, this application's oom_score will be 500 on A, 250 on B.
> 

Right.

> How admin detemine the best oom_score_adj value ? Does it depend on envrionment
> even if runnning the same application ?
> 

Yes, because the idea of /proc/pid/oom_score_adj is to allow userspace to 
both set priorities for oom killing and also define when a task has become 
a memory leaker (i.e. using far more memory than expected).  You can't use 
a quantity of memory to either prefer or bias an application because you 
don't know its memory usage in context of the system, memcg, mempolicy, or 
cpuset: a bias of 1G would mean "always kill this task" in a cpuset with a 
512MB node whereas it would mean relatively nothing on a 64GB machine.  
With a proportion, however, you could easily set a oom_score_adj of 250, 
for example, to say this application should be penalized 25% of available 
memory regardless of whether that's the entire system or a "virtual 
system" consisting of a cpuset, memcg, or mempolicy.

It would obviously be trivial to add another /proc/pid knob that would 
calculate the value for you given a quantity based on the memory 
constraints of pid, I'm not against that addition.

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