memcg: simplify LRU handling by new rule

Now, at LRU handling, memory cgroup needs to do complicated works to see
valid pc->mem_cgroup, which may be overwritten.

This patch is for relaxing the protocol. This patch guarantees
   - when pc->mem_cgroup is overwritten, page must not be on LRU.

By this, LRU routine can believe pc->mem_cgroup and don't need to check
bits on pc->flags.  This new rule may adds small overheads to swapin.  But
in most case, lru handling gets faster.

After this patch, PCG_ACCT_LRU bit is obsolete and removed.

[akpm@linux-foundation.org: remove unneeded VM_BUG_ON(), restore hannes's christmas tree]
[akpm@linux-foundation.org: clean up code comment]
[hughd@google.com: fix NULL mem_cgroup_try_charge]
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Miklos Szeredi <mszeredi@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Ying Han <yinghan@google.com>
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 0 insertions, 8 deletions

diff --git a/include/linux/page_cgroup.h b/include/linux/page_cgroup.h
index 1153095ee457..a2d11771c84b 100644
--- a/include/linux/page_cgroup.h
+++ b/include/linux/page_cgroup.h
@@ -10,8 +10,6 @@ enum {
         /* flags for mem_cgroup and file and I/O status */
         PCG_MOVE_LOCK, /* For race between move_account v.s. following bits */
         PCG_FILE_MAPPED, /* page is accounted as "mapped" */
-        /* No lock in page_cgroup */
-        PCG_ACCT_LRU, /* page has been accounted for (under lru_lock) */
         __NR_PCG_FLAGS,
 };
 
@@ -75,12 +73,6 @@ TESTPCGFLAG(Used, USED)
 CLEARPCGFLAG(Used, USED)
 SETPCGFLAG(Used, USED)
 
-SETPCGFLAG(AcctLRU, ACCT_LRU)
-CLEARPCGFLAG(AcctLRU, ACCT_LRU)
-TESTPCGFLAG(AcctLRU, ACCT_LRU)
-TESTCLEARPCGFLAG(AcctLRU, ACCT_LRU)
-
-
 SETPCGFLAG(FileMapped, FILE_MAPPED)
 CLEARPCGFLAG(FileMapped, FILE_MAPPED)
 TESTPCGFLAG(FileMapped, FILE_MAPPED)