linux-kernel - Re: [PATCH] mm: mlock: remove lru_add_drain

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Date:   Thu, 19 Oct 2017 14:18:59 +1100
From:   Balbir Singh <bsingharora@...il.com>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...e.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Minchan Kim <minchan@...nel.org>,
        Yisheng Xie <xieyisheng1@...wei.com>,
        Ingo Molnar <mingo@...nel.org>,
        Greg Thelen <gthelen@...gle.com>,
        Hugh Dickins <hughd@...gle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: mlock: remove lru_add_drain_all()

On Wed, 18 Oct 2017 16:17:30 -0700
Shakeel Butt <shakeelb@...gle.com> wrote:

> Recently we have observed high latency in mlock() in our generic
> library and noticed that users have started using tmpfs files even
> without swap and the latency was due to expensive remote LRU cache
> draining.
> 
> Is lru_add_drain_all() required by mlock()? The answer is no and the
> reason it is still in mlock() is to rapidly move mlocked pages to
> unevictable LRU. Without lru_add_drain_all() the mlocked pages which
> were on pagevec at mlock() time will be moved to evictable LRUs but
> will eventually be moved back to unevictable LRU by reclaim. So, we
> can safely remove lru_add_drain_all() from mlock(). Also there is no
> need for local lru_add_drain() as it will be called deep inside
> __mm_populate() (in follow_page_pte()).
> 
> Signed-off-by: Shakeel Butt <shakeelb@...gle.com>
> ---

Does this perturb statistics around LRU pages in cgroups and meminfo
about where the pages actually belong?

Balbir Singh.