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Commit a394cb8ee632ec5edce20309901ec66767497a43

Authored by Michal Hocko
Committed by Linus Torvalds
1 parent 4ca3a69bcb
Exists in smarc-l5.0.0_1.0.0-ga and in 5 other branches imx_3.10.17_1.0.1_ga, imx_3.10.53_1.1.0_ga, imx_3.14.28_1.0.0_ga, smarc-imx_3.10.53_1.1.0_ga, smarc-imx_3.14.28_1.0.0_ga

memcg,vmscan: do not break out targeted reclaim without reclaimed pages 

Targeted (hard resp soft) reclaim has traditionally tried to scan one
group with decreasing priority until nr_to_reclaim (SWAP_CLUSTER_MAX
pages) is reclaimed or all priorities are exhausted.  The reclaim is
then retried until the limit is met.

This approach, however, doesn't work well with deeper hierarchies where
groups higher in the hierarchy do not have any or only very few pages
(this usually happens if those groups do not have any tasks and they
have only re-parented pages after some of their children is removed).
Those groups are reclaimed with decreasing priority pointlessly as there
is nothing to reclaim from them.

An easiest fix is to break out of the memcg iteration loop in
shrink_zone only if the whole hierarchy has been visited or sufficient
pages have been reclaimed.  This is also more natural because the
reclaimer expects that the hierarchy under the given root is reclaimed.
As a result we can simplify the soft limit reclaim which does its own
iteration.

[yinghan@google.com: break out of the hierarchy loop only if nr_reclaimed exceeded nr_to_reclaim]
[akpm@linux-foundation.org: use conventional comparison order]
Signed-off-by: Michal Hocko <mhocko@suse.cz>
Reported-by: Ying Han <yinghan@google.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Tejun Heo <htejun@gmail.com>
Cc: Glauber Costa <glommer@parallels.com>
Cc: Li Zefan <lizefan@huawei.com>
Signed-off-by: Ying Han <yinghan@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Showing 1 changed file with 9 additions and 10 deletions Side-by-side Diff

... ... @@ -1973,18 +1973,17 @@
1973 1973 shrink_lruvec(lruvec, sc);
1974 1974  
1975 1975 /*
1976   - * Limit reclaim has historically picked one
1977   - * memcg and scanned it with decreasing
1978   - * priority levels until nr_to_reclaim had
1979   - * been reclaimed. This priority cycle is
1980   - * thus over after a single memcg.
1981   - *
1982   - * Direct reclaim and kswapd, on the other
1983   - * hand, have to scan all memory cgroups to
1984   - * fulfill the overall scan target for the
  1976 + * Direct reclaim and kswapd have to scan all memory
  1977 + * cgroups to fulfill the overall scan target for the
1985 1978 * zone.
  1979 + *
  1980 + * Limit reclaim, on the other hand, only cares about
  1981 + * nr_to_reclaim pages to be reclaimed and it will
  1982 + * retry with decreasing priority if one round over the
  1983 + * whole hierarchy is not sufficient.
1986 1984 */
1987   - if (!global_reclaim(sc)) {
  1985 + if (!global_reclaim(sc) &&
  1986 + sc->nr_reclaimed >= sc->nr_to_reclaim) {
1988 1987 mem_cgroup_iter_break(root, memcg);
1989 1988 break;
1990 1989 }