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After this patch, PCG_ACCT_LRU bit is obsolete and removed.

[[email protected]: remove unneeded VM_BUG_ON(), restore hannes's christmas tree]
[[email protected]: clean up code comment]
[[email protected]: fix NULL mem_cgroup_try_charge]
Signed-off-by: KAMEZAWA Hiroyuki <[email protected]>
Cc: Miklos Szeredi <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
Cc: Ying Han <[email protected]>
Signed-off-by: Hugh Dickins <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions