Re: [PATCH v5] mm/vmscan: more restrictive condition for retry in do_try_to_free_pages

[Johannes Weiner]

On Wed, Mar 22, 2017 at 10:11:33PM +0800, Yisheng Xie wrote:
> From: Yisheng Xie <xieyisheng1@xxxxxxxxxx>
> 
> By reviewing code, I find that when enter do_try_to_free_pages, the
> may_thrash is always clear, and it will retry shrink zones to tap
> cgroup's reserves memory by setting may_thrash when the former
> shrink_zones reclaim nothing.
> 
> However, when memcg is disabled or on legacy hierarchy, or there do not
> have any memcg protected by low limit, it should not do this useless
> retry at all, for we do not have any cgroup's reserves memory to tap,
> and we have already done hard work but made no progress, which as Michal
> pointed out in former version, we are trying hard to control the retry
> logical of page alloctor, and the current additional round of reclaim is
> just lame.
> 
> Therefore, to avoid this unneeded retrying and make code more readable,
> we remove the may_thrash field in scan_control, instead, introduce
> memcg_low_reclaim and memcg_low_skipped, and only retry when
> memcg_low_skipped, by setting memcg_low_reclaim.
> 
> Signed-off-by: Yisheng Xie <xieyisheng1@xxxxxxxxxx>
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> Suggested-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> Suggested-by: Michal Hocko <mhocko@xxxxxxxxxx>
> Suggested-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
> Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>

Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>

Thanks Yisheng!