On Sat 02-05-20 09:59:09, Yafang Shao wrote:
> A cgroup can have both memory protection and a memory limit to isolate
> it from its siblings in both directions - for example, to prevent it
> from being shrunk below 2G under high pressure from outside, but also
> from growing beyond 4G under low pressure.
>
> Commit 9783aa9917f8 ("mm, memcg: proportional memory.{low,min} reclaim")
> implemented proportional scan pressure so that multiple siblings in
> excess of their protection settings don't get reclaimed equally but
> instead in accordance to their unprotected portion.
>
> During limit reclaim, this proportionality shouldn't apply of course:
> there is no competition, all pressure is from within the cgroup and
> should be applied as such. Reclaim should operate at full efficiency.
>
> However, mem_cgroup_protected() never expected anybody to look at the
> effective protection values when it indicated that the cgroup is above
> its protection. As a result, a query during limit reclaim may return
> stale protection values that were calculated by a previous reclaim cycle
> in which the cgroup did have siblings.
>
> When this happens, reclaim is unnecessarily hesitant and potentially
> slow to meet the desired limit. In theory this could lead to premature
> OOM kills, although it's not obvious this has occurred in practice.
>
> [hannes@xxxxxxxxxxx: changelog]
> [mhocko@xxxxxxxxxx: rework code comment]
> [chris@xxxxxxxxxxxxxx: retitle]
> Fixes: 9783aa9917f8 ("mm, memcg: proportional memory.{low,min} reclaim")
> Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
> Acked-by: Roman Gushchin <guro@xxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Chris Down <chris@xxxxxxxxxxxxxx>
I have only now processed my inbox to this email. Please consider the
changelog part which explains the fix I have posted earlier this morning
http://lkml.kernel.org/r/20200504072342.GD22838@xxxxxxxxxxxxxx
Other than that
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
--
Michal Hocko
SUSE Labs
