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authorJohannes Weiner <hannes@cmpxchg.org>2011-03-24 02:42:26 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2011-03-24 05:46:26 +0300
commitad324e94475a04cfcdfdb11ad20f8ea81268e411 (patch)
tree4326bb602a3528071ffd6f3030c3a82c76a3454e /mm
parentf212ad7cf9c73f8a7fa160e223dcb3f074441a72 (diff)
downloadlinux-ad324e94475a04cfcdfdb11ad20f8ea81268e411.tar.xz
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>
Diffstat (limited to 'mm')
-rw-r--r--mm/memcontrol.c3
1 files changed, 0 insertions, 3 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 0356cb6c9504..5f7b0e1d789c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -370,9 +370,6 @@ page_cgroup_zoneinfo(struct page_cgroup *pc)
int nid = page_cgroup_nid(pc);
int zid = page_cgroup_zid(pc);
- if (!mem)
- return NULL;
-
return mem_cgroup_zoneinfo(mem, nid, zid);
}