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Subject[BUGFIX][PATCH v4] memcg: fix memory migration of shmem swapcache
> Sorry for nit-picking but succeed is not as good as succeeded,
> successful, successful_migration or migration_ok
>
OK, I use "migration_ok".

===
From: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>

In current implimentation, mem_cgroup_end_migration() decides whether the page
migration has succeeded or not by checking "oldpage->mapping".

But if we are tring to migrate a shmem swapcache, the page->mapping of it is
NULL from the begining, so the check would be invalid.
As a result, mem_cgroup_end_migration() assumes the migration has succeeded
even if it's not, so "newpage" would be freed while it's not uncharged.

This patch fixes it by passing mem_cgroup_end_migration() the result of the
page migration.

Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
v3->v4
- s/succeed/migration_ok
v2->v3
- s/success/succeed
v1->v2
- pass mem_cgroup_end_migration() "bool" instead of "int".
include/linux/memcontrol.h | 5 ++---
mm/memcontrol.c | 5 ++---
mm/migrate.c | 2 +-
3 files changed, 5 insertions(+), 7 deletions(-)
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 159a076..769c318 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -93,7 +93,7 @@ extern int
mem_cgroup_prepare_migration(struct page *page,
struct page *newpage, struct mem_cgroup **ptr);
extern void mem_cgroup_end_migration(struct mem_cgroup *mem,
- struct page *oldpage, struct page *newpage);
+ struct page *oldpage, struct page *newpage, bool migration_ok);

/*
* For memory reclaim.
@@ -231,8 +231,7 @@ mem_cgroup_prepare_migration(struct page *page, struct page *newpage,
}

static inline void mem_cgroup_end_migration(struct mem_cgroup *mem,
- struct page *oldpage,
- struct page *newpage)
+ struct page *oldpage, struct page *newpage, bool migration_ok)
{
}

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 61678be..c35f817 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2856,7 +2856,7 @@ int mem_cgroup_prepare_migration(struct page *page,

/* remove redundant charge if migration failed*/
void mem_cgroup_end_migration(struct mem_cgroup *mem,
- struct page *oldpage, struct page *newpage)
+ struct page *oldpage, struct page *newpage, bool migration_ok)
{
struct page *used, *unused;
struct page_cgroup *pc;
@@ -2865,8 +2865,7 @@ void mem_cgroup_end_migration(struct mem_cgroup *mem,
return;
/* blocks rmdir() */
cgroup_exclude_rmdir(&mem->css);
- /* at migration success, oldpage->mapping is NULL. */
- if (oldpage->mapping) {
+ if (!migration_ok) {
used = oldpage;
unused = newpage;
} else {
diff --git a/mm/migrate.c b/mm/migrate.c
index 6ae8a66..be66b23 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -756,7 +756,7 @@ rcu_unlock:
rcu_read_unlock();
uncharge:
if (!charge)
- mem_cgroup_end_migration(mem, page, newpage);
+ mem_cgroup_end_migration(mem, page, newpage, rc == 0);
unlock:
unlock_page(page);

--
1.7.1


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