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From:   "Huang, Ying" <ying.huang@intel.com>
To:     Jianlin Lv <iecedge@gmail.com>
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Subject: Re: [PATCH] memcg: add interface to force disable swap
References: <20231007130905.78554-1-jianlv@ebay.com>
        <87mswtkj8x.fsf@yhuang6-desk2.ccr.corp.intel.com>
        <CAFA-uR9ymPTktMbi96cb+smjQHB4Y=8SQfAqmsqTbniGbkGTLA@mail.gmail.com>
        <87il7hjzdp.fsf@yhuang6-desk2.ccr.corp.intel.com>
        <CAFA-uR9n-rKw4k26Bhm=P16jOMtAncRsno7o=yYJ1kTxmB_mRw@mail.gmail.com>
Date:   Mon, 09 Oct 2023 13:58:10 +0800
In-Reply-To: <CAFA-uR9n-rKw4k26Bhm=P16jOMtAncRsno7o=yYJ1kTxmB_mRw@mail.gmail.com>
        (Jianlin Lv's message of "Sun, 8 Oct 2023 17:34:44 +0800")
Message-ID: <87edi4jq19.fsf@yhuang6-desk2.ccr.corp.intel.com>
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Jianlin Lv <iecedge@gmail.com> writes:

> On Sun, Oct 8, 2023 at 4:26=E2=80=AFPM Huang, Ying <ying.huang@intel.com>=
 wrote:
>>
>> Jianlin Lv <iecedge@gmail.com> writes:
>>
>> > On Sun, Oct 8, 2023 at 9:17=E2=80=AFAM Huang, Ying <ying.huang@intel.c=
om> wrote:
>> >>
>> >> Jianlin Lv <iecedge@gmail.com> writes:
>> >>
>> >> > From: Jianlin Lv <iecedge@gmail.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 swappines=
s is
>> > set to 0 in the production environment through the following test prog=
ram.
>> > Not sure whether this program can reproduce the issue in any environme=
nt.
>> >
>> > From the implementation of the get_scan_count code, it can be seen tha=
t,
>> > 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 introduc=
es
>> > uncertainty.
>> >
>> > For the JVM issue at hand, we expect deterministic SCAN_FILE scan to a=
void
>> > 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 =3D=3D 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