Re: [patch 06/19] mm: memcontrol: prevent starvation when writing memory.high

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On Sat, Jan 23, 2021 at 9:01 PM Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> From: Johannes Weiner <hannes@xxxxxxxxxxx>
> Subject: mm: memcontrol: prevent starvation when writing memory.high
>
> When a value is written to a cgroup's memory.high control file, the
> write() context first tries to reclaim the cgroup to size before putting
> the limit in place for the workload.  Concurrent charges from the workload
> can keep such a write() looping in reclaim indefinitely.
>
> In the past, a write to memory.high would first put the limit in place for
> the workload, then do targeted reclaim until the new limit has been met -
> similar to how we do it for memory.max.  This wasn't prone to the
> described starvation issue.  However, this sequence could cause excessive
> latencies in the workload, when allocating threads could be put into long
> penalty sleeps on the sudden memory.high overage created by the write(),
> before that had a chance to work it off.
>
> Now that memory_high_write() performs reclaim before enforcing the new
> limit, reflect that the cgroup may well fail to converge due to concurrent
> workload activity.  Bail out of the loop after a few tries.
>
> Link: https://lkml.kernel.org/r/20210112163011.127833-1-hannes@xxxxxxxxxxx
> Fixes: 536d3bf261a2 ("mm: memcontrol: avoid workload stalls when lowering memory.high")
> Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
> Reported-by: Tejun Heo <tj@xxxxxxxxxx>
> Acked-by: Roman Gushchin <guro@xxxxxx>
> Reviewed-by: Michal Koutný <mkoutny@xxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>    [5.8+]
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>

Johannes requested to replace this patch with
https://lore.kernel.org/linux-mm/20210122184341.292461-1-hannes@xxxxxxxxxxx/




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