linux-kernel - Re: [PATCH v5] mm/vmscan: more restrictive condition for retry in do_try_to_free

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Date:   Wed, 22 Mar 2017 10:43:49 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Yisheng Xie <ysxie@...mail.com>
Cc:     akpm@...ux-foundation.org, mgorman@...e.de, vbabka@...e.cz,
        mhocko@...e.com, riel@...hat.com, shakeelb@...gle.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        xieyisheng1@...wei.com, guohanjun@...wei.com, qiuxishi@...wei.com
Subject: Re: [PATCH v5] mm/vmscan: more restrictive condition for retry in
 do_try_to_free_pages

On Wed, Mar 22, 2017 at 10:11:33PM +0800, Yisheng Xie wrote:
> From: Yisheng Xie <xieyisheng1@...wei.com>
> 
> 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@...wei.com>
> Acked-by: Michal Hocko <mhocko@...e.com>
> Suggested-by: Johannes Weiner <hannes@...xchg.org>
> Suggested-by: Michal Hocko <mhocko@...nel.org>
> Suggested-by: Shakeel Butt <shakeelb@...gle.com>
> Reviewed-by: Shakeel Butt <shakeelb@...gle.com>

Acked-by: Johannes Weiner <hannes@...xchg.org>

Thanks Yisheng!