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memcg: add mem_cgroup_replace_page_cache() to fix LRU issue

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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 <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: Miklos Szeredi <mszeredi@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
KAMEZAWA Hiroyuki
2012-01-12 17:17:44 -08:00
committed by Linus Torvalds
parent 28d82dc1c4
commit ab936cbcd0
3 changed files with 52 additions and 16 deletions
Download Patch File Download Diff File Expand all files Collapse all files
mm/filemap.c
+2 -16
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@@ -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;
VM_BUG_ON(!PageLocked(old));
VM_BUG_ON(!PageLocked(new));
VM_BUG_ON(new->mapping);
/*
* 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);
spin_unlock_irq(&mapping->tree_lock);
/* mem_cgroup codes must not be called under tree_lock */
mem_cgroup_replace_page_cache(old, new);
radix_tree_preload_end();
if (freepage)
freepage(old);
page_cache_release(old);
mem_cgroup_end_migration(memcg, old, new, true);
} else {
mem_cgroup_end_migration(memcg, old, new, false);
}
return error;