path: root/mm/filemap.c
diff options
authorKAMEZAWA Hiroyuki <>2012-01-12 17:17:44 -0800
committerLinus Torvalds <>2012-01-12 20:13:04 -0800
commitab936cbcd02072a34b60d268f94440fd5cf1970b (patch)
treed37e3e3c54cc4cc691a428b6ceb71b4b40e4f42b /mm/filemap.c
parent28d82dc1c4edbc352129f97f4ca22624d1fe61de (diff)
memcg: add mem_cgroup_replace_page_cache() to fix LRU issue
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 <> Cc: <> Signed-off-by: Andrew Morton <> Signed-off-by: Linus Torvalds <>
Diffstat (limited to 'mm/filemap.c')
1 files changed, 2 insertions, 16 deletions
diff --git a/mm/filemap.c b/mm/filemap.c
index c4ee2e918bea..97f49ed35bd2 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;