path: root/mm
diff options
authorKAMEZAWA Hiroyuki <>2012-01-12 17:17:44 -0800
committerGreg Kroah-Hartman <>2012-01-18 07:31:58 -0800
commit8d0120df91823df951facd3527e9f148b24e78f3 (patch)
tree4ec77b5fcf0ee1be4d6cbe4c79ff9ac6157eb7d5 /mm
parentc877bca3e2a5ded480a824c1999d0eb526a29f2a (diff)
memcg: add mem_cgroup_replace_page_cache() to fix LRU issue
commit ab936cbcd02072a34b60d268f94440fd5cf1970b upstream. Commit ef6a3c6311 ("mm: add replace_page_cache_page() function") added a function replace_page_cache_page(). This function replaces a page in the radix-tree with a new page. WHen doing this, memory cgroup needs to fix up the accounting information. memcg need to check PCG_USED bit etc. In some(many?) cases, 'newpage' is on LRU before calling replace_page_cache(). So, memcg's LRU accounting information should be fixed, too. This patch adds mem_cgroup_replace_page_cache() and removes the old hooks. In that function, old pages will be unaccounted without touching res_counter and new page will be accounted to the memcg (of old page). WHen overwriting pc->mem_cgroup of newpage, take zone->lru_lock and avoid races with LRU handling. Background: replace_page_cache_page() is called by FUSE code in its splice() handling. Here, 'newpage' is replacing oldpage but this newpage is not a newly allocated page and may be on LRU. LRU mis-accounting will be critical for memory cgroup because rmdir() checks the whole LRU is empty and there is no account leak. If a page is on the other LRU than it should be, rmdir() will fail. This bug was added in March 2011, but no bug report yet. I guess there are not many people who use memcg and FUSE at the same time with upstream kernels. The result of this bug is that admin cannot destroy a memcg because of account leak. So, no panic, no deadlock. And, even if an active cgroup exist, umount can succseed. So no problem at shutdown. Signed-off-by: KAMEZAWA Hiroyuki <> Acked-by: Johannes Weiner <> Acked-by: Michal Hocko <> Cc: Miklos Szeredi <> Cc: Hugh Dickins <> Signed-off-by: Andrew Morton <> Signed-off-by: Linus Torvalds <> Signed-off-by: Greg Kroah-Hartman <>
Diffstat (limited to 'mm')
2 files changed, 46 insertions, 16 deletions
diff --git a/mm/filemap.c b/mm/filemap.c
index b91f3aa627fc..0eedbf85062d 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -393,24 +393,11 @@ EXPORT_SYMBOL(filemap_write_and_wait_range);
int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
int error;
- struct mem_cgroup *memcg = NULL;
- /*
- * This is not page migration, but prepare_migration and
- * end_migration does enough work for charge replacement.
- *
- * In the longer term we probably want a specialized function
- * for moving the charge from old to new in a more efficient
- * manner.
- */
- error = mem_cgroup_prepare_migration(old, new, &memcg, gfp_mask);
- if (error)
- return error;
error = radix_tree_preload(gfp_mask & ~__GFP_HIGHMEM);
if (!error) {
struct address_space *mapping = old->mapping;
@@ -432,13 +419,12 @@ int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
if (PageSwapBacked(new))
__inc_zone_page_state(new, NR_SHMEM);
+ /* mem_cgroup codes must not be called under tree_lock */
+ mem_cgroup_replace_page_cache(old, new);
if (freepage)
- mem_cgroup_end_migration(memcg, old, new, true);
- } else {
- mem_cgroup_end_migration(memcg, old, new, false);
return error;
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index afde618f9895..dd81ddc64b4d 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3355,6 +3355,50 @@ void mem_cgroup_end_migration(struct mem_cgroup *mem,
+ * At replace page cache, newpage is not under any memcg but it's on
+ * LRU. So, this function doesn't touch res_counter but handles LRU
+ * in correct way. Both pages are locked so we cannot race with uncharge.
+ */
+void mem_cgroup_replace_page_cache(struct page *oldpage,
+ struct page *newpage)
+ struct mem_cgroup *memcg;
+ struct page_cgroup *pc;
+ struct zone *zone;
+ enum charge_type type = MEM_CGROUP_CHARGE_TYPE_CACHE;
+ unsigned long flags;
+ if (mem_cgroup_disabled())
+ return;
+ pc = lookup_page_cgroup(oldpage);
+ /* fix accounting on old pages */
+ lock_page_cgroup(pc);
+ memcg = pc->mem_cgroup;
+ mem_cgroup_charge_statistics(memcg, PageCgroupCache(pc), -1);
+ ClearPageCgroupUsed(pc);
+ unlock_page_cgroup(pc);
+ if (PageSwapBacked(oldpage))
+ zone = page_zone(newpage);
+ pc = lookup_page_cgroup(newpage);
+ /*
+ * Even if newpage->mapping was NULL before starting replacement,
+ * the newpage may be on LRU(or pagevec for LRU) already. We lock
+ * LRU while we overwrite pc->mem_cgroup.
+ */
+ spin_lock_irqsave(&zone->lru_lock, flags);
+ if (PageLRU(newpage))
+ del_page_from_lru_list(zone, newpage, page_lru(newpage));
+ __mem_cgroup_commit_charge(memcg, newpage, 1, pc, type);
+ if (PageLRU(newpage))
+ add_page_to_lru_list(zone, newpage, page_lru(newpage));
+ spin_unlock_irqrestore(&zone->lru_lock, flags);
static struct page_cgroup *lookup_page_cgroup_used(struct page *page)