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memcg: no uncharged pages reach page_cgroup_zoneinfo 

This patch series removes the direct page pointer from struct page_cgroup,
which saves 20% of per-page memcg memory overhead (Fedora and Ubuntu
enable memcg per default, openSUSE apparently too).

The node id or section number is encoded in the remaining free bits of
pc->flags which allows calculating the corresponding page without the
extra pointer.

I ran, what I think is, a worst-case microbenchmark that just cats a large
sparse file to /dev/null, because it means that walking the LRU list on
behalf of per-cgroup reclaim and looking up pages from page_cgroups is
happening constantly and at a high rate.  But it made no measurable
difference.  A profile reported a 0.11% share of the new
lookup_cgroup_page() function in this benchmark.

This patch:

All callsites check PCG_USED before passing pc->mem_cgroup, so the latter
is never NULL.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Minchan Kim <minchan.kim@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Johannes Weiner 2011-03-23 16:42:26 -07:00 committed by Linus Torvalds
parent f212ad7cf9
commit ad324e9447
1 changed files with 0 additions and 3 deletions
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3
mm/memcontrol.c
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@ -370,9 +370,6 @@ page_cgroup_zoneinfo(struct page_cgroup *pc)
int nid = page_cgroup_nid(pc); int nid = page_cgroup_nid(pc);
int zid = page_cgroup_zid(pc); int zid = page_cgroup_zid(pc);
if (!mem)
return NULL;
return mem_cgroup_zoneinfo(mem, nid, zid); return mem_cgroup_zoneinfo(mem, nid, zid);
} }