[PATCH 1/3] ksm: clean up obsolete references

[PATCH 1/3] ksm: clean up obsolete references

[Hugh Dickins]

A few cleanups, given the munlock fix: the comment on ksm_test_exit()
no longer applies, and it can be made private to ksm.c; there's no
more reference to mmu_gather or tlb.h, and mmap.c doesn't need ksm.h.

Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
---

 include/linux/ksm.h |   20 --------------------
 mm/ksm.c            |   14 +++++++++++++-
 mm/mmap.c           |    1 -
 3 files changed, 13 insertions(+), 22 deletions(-)

--- mmotm/include/linux/ksm.h	2009-09-05 14:40:16.000000000 +0100
+++ linux/include/linux/ksm.h	2009-09-05 16:41:55.000000000 +0100
@@ -12,8 +12,6 @@
 #include <linux/sched.h>
 #include <linux/vmstat.h>
 
-struct mmu_gather;
-
 #ifdef CONFIG_KSM
 int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
 		unsigned long end, int advice, unsigned long *vm_flags);
@@ -27,19 +25,6 @@ static inline int ksm_fork(struct mm_str
 	return 0;
 }
 
-/*
- * For KSM to handle OOM without deadlock when it's breaking COW in a
- * likely victim of the OOM killer, exit_mmap() has to serialize with
- * ksm_exit() after freeing mm's pages but before freeing its page tables.
- * That leaves a window in which KSM might refault pages which have just
- * been finally unmapped: guard against that with ksm_test_exit(), and
- * use it after getting mmap_sem in ksm.c, to check if mm is exiting.
- */
-static inline bool ksm_test_exit(struct mm_struct *mm)
-{
-	return atomic_read(&mm->mm_users) == 0;
-}
-
 static inline void ksm_exit(struct mm_struct *mm)
 {
 	if (test_bit(MMF_VM_MERGEABLE, &mm->flags))
@@ -78,11 +63,6 @@ static inline int ksm_fork(struct mm_str
 {
 	return 0;
 }
-
-static inline bool ksm_test_exit(struct mm_struct *mm)
-{
-	return 0;
-}
 
 static inline void ksm_exit(struct mm_struct *mm)
 {
--- mmotm/mm/ksm.c	2009-09-05 14:40:16.000000000 +0100
+++ linux/mm/ksm.c	2009-09-05 16:41:55.000000000 +0100
@@ -32,7 +32,6 @@
 #include <linux/mmu_notifier.h>
 #include <linux/ksm.h>
 
-#include <asm/tlb.h>
 #include <asm/tlbflush.h>
 
 /*
@@ -285,6 +284,19 @@ static inline int in_stable_tree(struct
 }
 
 /*
+ * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
+ * page tables after it has passed through ksm_exit() - which, if necessary,
+ * takes mmap_sem briefly to serialize against them.  ksm_exit() does not set
+ * a special flag: they can just back out as soon as mm_users goes to zero.
+ * ksm_test_exit() is used throughout to make this test for exit: in some
+ * places for correctness, in some places just to avoid unnecessary work.
+ */
+static inline bool ksm_test_exit(struct mm_struct *mm)
+{
+	return atomic_read(&mm->mm_users) == 0;
+}
+
+/*
  * We use break_ksm to break COW on a ksm page: it's a stripped down
  *
  *	if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1)
--- mmotm/mm/mmap.c	2009-09-05 14:40:16.000000000 +0100
+++ linux/mm/mmap.c	2009-09-05 16:41:55.000000000 +0100
@@ -27,7 +27,6 @@
 #include <linux/mount.h>
 #include <linux/mempolicy.h>
 #include <linux/rmap.h>
-#include <linux/ksm.h>
 #include <linux/mmu_notifier.h>
 #include <linux/perf_counter.h>
 #include <linux/hugetlb.h>

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[PATCH 2/3] ksm: unmerge is an origin of OOMs

[Hugh Dickins]

Just as the swapoff system call allocates many pages of RAM to various
processes, perhaps triggering OOM, so "echo 2 >/sys/kernel/mm/ksm/run"
(unmerge) is liable to allocate many pages of RAM to various processes,
perhaps triggering OOM; and each is normally run from a modest admin
process (swapoff or shell), easily repeated until it succeeds.

So treat unmerge_and_remove_all_rmap_items() in the same way that we
treat try_to_unuse(): generalize PF_SWAPOFF to PF_OOM_ORIGIN, and
bracket both with that, to ask the OOM killer to kill them first,
to prevent them from spawning more and more OOM kills.

Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
---

 include/linux/sched.h |    2 +-
 mm/ksm.c              |    2 ++
 mm/oom_kill.c         |    2 +-
 mm/swapfile.c         |    4 ++--
 4 files changed, 6 insertions(+), 4 deletions(-)

--- mmotm/include/linux/sched.h	2009-09-05 14:40:16.000000000 +0100
+++ linux/include/linux/sched.h	2009-09-05 16:41:55.000000000 +0100
@@ -1755,7 +1755,7 @@ extern cputime_t task_gtime(struct task_
 #define PF_FROZEN	0x00010000	/* frozen for system suspend */
 #define PF_FSTRANS	0x00020000	/* inside a filesystem transaction */
 #define PF_KSWAPD	0x00040000	/* I am kswapd */
-#define PF_SWAPOFF	0x00080000	/* I am in swapoff */
+#define PF_OOM_ORIGIN	0x00080000	/* Allocating much memory to others */
 #define PF_LESS_THROTTLE 0x00100000	/* Throttle me less: I clean memory */
 #define PF_KTHREAD	0x00200000	/* I am a kernel thread */
 #define PF_RANDOMIZE	0x00400000	/* randomize virtual address space */
--- mmotm/mm/ksm.c	2009-09-05 14:40:16.000000000 +0100
+++ linux/mm/ksm.c	2009-09-05 16:41:55.000000000 +0100
@@ -1564,7 +1564,9 @@ static ssize_t run_store(struct kobject
 	if (ksm_run != flags) {
 		ksm_run = flags;
 		if (flags & KSM_RUN_UNMERGE) {
+			current->flags |= PF_OOM_ORIGIN;
 			err = unmerge_and_remove_all_rmap_items();
+			current->flags &= ~PF_OOM_ORIGIN;
 			if (err) {
 				ksm_run = KSM_RUN_STOP;
 				count = err;
--- mmotm/mm/oom_kill.c	2009-09-05 14:40:16.000000000 +0100
+++ linux/mm/oom_kill.c	2009-09-05 16:41:55.000000000 +0100
@@ -103,7 +103,7 @@ unsigned long badness(struct task_struct
 	/*
 	 * swapoff can easily use up all memory, so kill those first.
 	 */
-	if (p->flags & PF_SWAPOFF)
+	if (p->flags & PF_OOM_ORIGIN)
 		return ULONG_MAX;
 
 	/*
--- mmotm/mm/swapfile.c	2009-09-05 14:40:16.000000000 +0100
+++ linux/mm/swapfile.c	2009-09-05 16:41:55.000000000 +0100
@@ -1573,9 +1573,9 @@ SYSCALL_DEFINE1(swapoff, const char __us
 	p->flags &= ~SWP_WRITEOK;
 	spin_unlock(&swap_lock);
 
-	current->flags |= PF_SWAPOFF;
+	current->flags |= PF_OOM_ORIGIN;
 	err = try_to_unuse(type);
-	current->flags &= ~PF_SWAPOFF;
+	current->flags &= ~PF_OOM_ORIGIN;
 
 	if (err) {
 		/* re-insert swap space back into swap_list */

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Re: [PATCH 2/3] ksm: unmerge is an origin of OOMs

[Izik Eidus]

Hugh Dickins wrote:
> Just as the swapoff system call allocates many pages of RAM to various
> processes, perhaps triggering OOM, so "echo 2 >/sys/kernel/mm/ksm/run"
> (unmerge) is liable to allocate many pages of RAM to various processes,
> perhaps triggering OOM; and each is normally run from a modest admin
> process (swapoff or shell), easily repeated until it succeeds.
>
> So treat unmerge_and_remove_all_rmap_items() in the same way that we
> treat try_to_unuse(): generalize PF_SWAPOFF to PF_OOM_ORIGIN, and
> bracket both with that, to ask the OOM killer to kill them first,
> to prevent them from spawning more and more OOM kills.
>
> Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
> ---
>   

Acked-by: Izik Eidus <ieidus@redhat.com>

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Re: [PATCH 2/3] ksm: unmerge is an origin of OOMs

[Izik Eidus]

Hugh Dickins wrote:
> Just as the swapoff system call allocates many pages of RAM to various
> processes, perhaps triggering OOM, so "echo 2 >/sys/kernel/mm/ksm/run"
> (unmerge) is liable to allocate many pages of RAM to various processes,
> perhaps triggering OOM; and each is normally run from a modest admin
> process (swapoff or shell), easily repeated until it succeeds.
>
> So treat unmerge_and_remove_all_rmap_items() in the same way that we
> treat try_to_unuse(): generalize PF_SWAPOFF to PF_OOM_ORIGIN, and
> bracket both with that, to ask the OOM killer to kill them first,
> to prevent them from spawning more and more OOM kills.
>
> Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
> ---
>   

Acked-by: Izik Eidus <ieidus@redhat.com>

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[PATCH 3/3] ksm: mremap use err from ksm_madvise

[Hugh Dickins]

mremap move's use of ksm_madvise() was assuming -ENOMEM on failure,
because ksm_madvise used to say -EAGAIN for that; but ksm_madvise now
says -ENOMEM (letting madvise convert that to -EAGAIN), and can also
say -ERESTARTSYS when signalled: so pass the error from ksm_madvise.

Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
---

 mm/mremap.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

--- mmotm/mm/mremap.c	2009-09-05 14:40:16.000000000 +0100
+++ linux/mm/mremap.c	2009-09-05 16:41:55.000000000 +0100
@@ -175,6 +175,7 @@ static unsigned long move_vma(struct vm_
 	unsigned long excess = 0;
 	unsigned long hiwater_vm;
 	int split = 0;
+	int err;
 
 	/*
 	 * We'd prefer to avoid failure later on in do_munmap:
@@ -190,9 +191,10 @@ static unsigned long move_vma(struct vm_
 	 * pages recently unmapped.  But leave vma->vm_flags as it was,
 	 * so KSM can come around to merge on vma and new_vma afterwards.
 	 */
-	if (ksm_madvise(vma, old_addr, old_addr + old_len,
-						MADV_UNMERGEABLE, &vm_flags))
-		return -ENOMEM;
+	err = ksm_madvise(vma, old_addr, old_addr + old_len,
+						MADV_UNMERGEABLE, &vm_flags);
+	if (err)
+		return err;
 
 	new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
 	new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff);

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Re: [PATCH 3/3] ksm: mremap use err from ksm_madvise

[Izik Eidus]

Hugh Dickins wrote:
> mremap move's use of ksm_madvise() was assuming -ENOMEM on failure,
> because ksm_madvise used to say -EAGAIN for that; but ksm_madvise now
> says -ENOMEM (letting madvise convert that to -EAGAIN), and can also
> say -ERESTARTSYS when signalled: so pass the error from ksm_madvise.
>
> Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
> ---
>   
Acked-by: Izik Eidus <ieidus@redhat.com>

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Re: [PATCH 1/3] ksm: clean up obsolete references

[Izik Eidus]

Hugh Dickins wrote:
> A few cleanups, given the munlock fix: the comment on ksm_test_exit()
> no longer applies, and it can be made private to ksm.c; there's no
> more reference to mmu_gather or tlb.h, and mmap.c doesn't need ksm.h.
>
> Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
> ---
>
>   
Acked-by: Izik Eidus <ieidus@redhat.com>

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