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

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Message-ID: <CAFA-uR9n-rKw4k26Bhm=P16jOMtAncRsno7o=yYJ1kTxmB_mRw@mail.gmail.com>
Date:   Sun, 8 Oct 2023 17:34:44 +0800
From:   Jianlin Lv <iecedge@...il.com>
To:     "Huang, Ying" <ying.huang@...el.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

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.

>
> --
> Best Regards,
> Huang, Ying