linux-kernel - Re: [PATCH v2] mm: vmscan: reclaim anon pages if there are swapcache pages

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Message-ID: <ZOYFydIp3q8BNrEa@dhcp22.suse.cz>
Date:   Wed, 23 Aug 2023 15:12:41 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Liu Shixin <liushixin2@...wei.com>
Cc:     Yosry Ahmed <yosryahmed@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Shakeel Butt <shakeelb@...gle.com>,
        Muchun Song <muchun.song@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>,
        wangkefeng.wang@...wei.com, linux-kernel@...r.kernel.org,
        cgroups@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2] mm: vmscan: reclaim anon pages if there are swapcache
 pages

On Wed 23-08-23 10:00:58, Liu Shixin wrote:
> 
> 
> On 2023/8/23 0:35, Yosry Ahmed wrote:
> > On Mon, Aug 21, 2023 at 6:54 PM Liu Shixin <liushixin2@...wei.com> wrote:
> >> When spaces of swap devices are exhausted, only file pages can be reclaimed.
> >> But there are still some swapcache pages in anon lru list. This can lead
> >> to a premature out-of-memory.
> >>
> >> This problem can be fixed by checking number of swapcache pages in
> >> can_reclaim_anon_pages(). For memcg v2, there are swapcache stat that can
> >> be used directly. For memcg v1, use total_swapcache_pages() instead, which
> >> may not accurate but can solve the problem.
> > Interesting find. I wonder if we really don't have any handling of
> > this situation.
> I have alreadly test this problem and can confirm that it is a real problem.
> With 9MB swap space and 10MB mem_cgroup limit，when allocate 15MB memory,
> there is a probability that OOM occurs.

Could you be more specific about the test and the oom report?

-- 
Michal Hocko
SUSE Labs