[PATCH 1/2] memcg: rename and export try_get_mem_cgroup_from_page()

[Wu Fengguang <fengguang.wu@intel.com>]

So that the hwpoison injector can get mem_cgroup for arbitrary page
and thus know whether it is owned by some mem_cgroup task(s).

Background:

The hwpoison test suite need to inject hwpoison to a collection of
selected task pages, and must not touch pages not owned by these pages
and thus kill important system processes such as init. (But it's OK to
mis-hwpoison free/unowned pages as well as shared clean pages.
Mis-hwpoison of shared dirty pages will kill all tasks, so the test
suite will target all or non of such tasks in the first place.)

The memory cgroup serves this purpose well. We can put the target
processes under the control of a memory cgroup, and tell the hwpoison
injection code to only kill pages associated with some active memory
cgroup.

The prerequsite for doing hwpoison stress tests with mem_cgroup is,
the mem_cgroup code tracks task pages _accurately_ (unless page is
locked).  Which we believe is/should be true.

The benifits are simplification of hwpoison injector code. Also the
mem_cgroup code will automatically be tested by hwpoison test cases.

CC: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
CC: Hugh Dickins <hugh@veritas.com>
CC: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
CC: Balbir Singh <balbir@linux.vnet.ibm.com>
CC: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
 include/linux/memcontrol.h |    6 ++++++
 mm/memcontrol.c            |   12 +++++-------
 2 files changed, 11 insertions(+), 7 deletions(-)

--- linux-mm.orig/mm/memcontrol.c	2009-09-11 18:51:14.000000000 +0800
+++ linux-mm/mm/memcontrol.c	2009-09-11 18:52:14.000000000 +0800
@@ -1389,25 +1389,22 @@ static struct mem_cgroup *mem_cgroup_loo
 	return container_of(css, struct mem_cgroup, css);
 }
 
-static struct mem_cgroup *try_get_mem_cgroup_from_swapcache(struct page *page)
+struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page)
 {
-	struct mem_cgroup *mem;
+	struct mem_cgroup *mem = NULL;
 	struct page_cgroup *pc;
 	unsigned short id;
 	swp_entry_t ent;
 
 	VM_BUG_ON(!PageLocked(page));
 
-	if (!PageSwapCache(page))
-		return NULL;
-
 	pc = lookup_page_cgroup(page);
 	lock_page_cgroup(pc);
 	if (PageCgroupUsed(pc)) {
 		mem = pc->mem_cgroup;
 		if (mem && !css_tryget(&mem->css))
 			mem = NULL;
-	} else {
+	} else if (PageSwapCache(page)) {
 		ent.val = page_private(page);
 		id = lookup_swap_cgroup(ent);
 		rcu_read_lock();
@@ -1419,6 +1416,7 @@ static struct mem_cgroup *try_get_mem_cg
 	unlock_page_cgroup(pc);
 	return mem;
 }
+EXPORT_SYMBOL(try_get_mem_cgroup_from_page);
 
 /*
  * commit a charge got by __mem_cgroup_try_charge() and makes page_cgroup to be
@@ -1753,7 +1751,7 @@ int mem_cgroup_try_charge_swapin(struct 
 	 */
 	if (!PageSwapCache(page))
 		return 0;
-	mem = try_get_mem_cgroup_from_swapcache(page);
+	mem = try_get_mem_cgroup_from_page(page);
 	if (!mem)
 		goto charge_cur_mm;
 	*ptr = mem;
--- linux-mm.orig/include/linux/memcontrol.h	2009-09-11 18:51:13.000000000 +0800
+++ linux-mm/include/linux/memcontrol.h	2009-09-11 18:52:14.000000000 +0800
@@ -68,6 +68,7 @@ extern unsigned long mem_cgroup_isolate_
 extern void mem_cgroup_out_of_memory(struct mem_cgroup *mem, gfp_t gfp_mask);
 int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *mem);
 
+extern struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page);
 extern struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p);
 
 static inline
@@ -189,6 +190,11 @@ mem_cgroup_move_lists(struct page *page,
 {
 }
 
+static inline struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page)
+{
+	return NULL;
+}
+
 static inline int mm_match_cgroup(struct mm_struct *mm, struct mem_cgroup *mem)
 {
 	return 1;

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>