linux-kernel - Re: [PATCH] memcg: add interface to force disable swap

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Message-ID: <87edi4jq19.fsf@yhuang6-desk2.ccr.corp.intel.com>
Date:   Mon, 09 Oct 2023 13:58:10 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     Jianlin Lv <iecedge@...il.com>
Cc:     tj@...nel.org, lizefan.x@...edance.com, hannes@...xchg.org,
        corbet@....net, mhocko@...nel.org, roman.gushchin@...ux.dev,
        shakeelb@...gle.com, muchun.song@...ux.dev,
        akpm@...ux-foundation.org, yosryahmed@...gle.com,
        willy@...radead.org, linmiaohe@...wei.com,
        wangkefeng.wang@...wei.com, laoar.shao@...il.com,
        yuzhao@...gle.com, wuyun.abel@...edance.com, david@...hat.com,
        peterx@...hat.com, vishal.moola@...il.com, hughd@...gle.com,
        cgroups@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org, jianlv@...y.com
Subject: Re: [PATCH] memcg: add interface to force disable swap

Jianlin Lv <iecedge@...il.com> writes:

> On Sun, Oct 8, 2023 at 4:26 PM Huang, Ying <ying.huang@...el.com> wrote:
>>
>> Jianlin Lv <iecedge@...il.com> writes:
>>
>> > On Sun, Oct 8, 2023 at 9:17 AM Huang, Ying <ying.huang@...el.com> wrote:
>> >>
>> >> Jianlin Lv <iecedge@...il.com> writes:
>> >>
>> >> > From: Jianlin Lv <iecedge@...il.com>
>> >> >
>> >> > Global reclaim will swap even if swappiness is set to 0.
>> >>
>> >> Why?  Can you elaborate the situation?
>> >
>> > We reproduced the issue of pages being swapped out even when swappiness is
>> > set to 0 in the production environment through the following test program.
>> > Not sure whether this program can reproduce the issue in any environment.
>> >
>> > From the implementation of the get_scan_count code, it can be seen that,
>> > based on the current runtime situation, memory reclamation will choose a
>> > scanning method (SCAN_ANON/SCAN_FILE/SCAN_FRACT) to determine how
>> > aggressively the anon and file LRU are scanned. However, this introduces
>> > uncertainty.
>> >
>> > For the JVM issue at hand, we expect deterministic SCAN_FILE scan to avoid
>> > swapping out anon pages.
>>
>> Why doesn't memory.swap.max work?
>
> The main reason is that deployed nodes  are kept on cgroups v1.

Check the code again.  IIUC, for swappiness == 0, anonymous pages will
only be reclaimed if sc->file_is_tiny is true.  If we don't swap in that
situation, OOM may be triggerred.  I don't think that it's a good idea
to do that.  Or I miss something?

--
Best Regards,
Huang, Ying