linux-ext4 - Re: mm: mkfs.ext4 invoked oom-killer on i386

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Date:   Thu, 18 Jun 2020 22:59:28 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     Chris Down <chris@...isdown.name>
Cc:     Naresh Kamboju <naresh.kamboju@...aro.org>,
        Michal Hocko <mhocko@...nel.org>,
        Anders Roxell <anders.roxell@...aro.org>,
        "Linux F2FS DEV, Mailing List" 
        <linux-f2fs-devel@...ts.sourceforge.net>,
        linux-ext4 <linux-ext4@...r.kernel.org>,
        linux-block <linux-block@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        open list <linux-kernel@...r.kernel.org>,
        Linux-Next Mailing List <linux-next@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>, Arnd Bergmann <arnd@...db.de>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        "Theodore Ts'o" <tytso@....edu>, Chao Yu <chao@...nel.org>,
        Hugh Dickins <hughd@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Chao Yu <yuchao0@...wei.com>, lkft-triage@...ts.linaro.org,
        Johannes Weiner <hannes@...xchg.org>,
        Roman Gushchin <guro@...com>, Cgroups <cgroups@...r.kernel.org>
Subject: Re: mm: mkfs.ext4 invoked oom-killer on i386 - pagecache_get_page

On Thu, Jun 18, 2020 at 8:37 PM Chris Down <chris@...isdown.name> wrote:
>
> Yafang Shao writes:
> >On Thu, Jun 18, 2020 at 5:09 AM Chris Down <chris@...isdown.name> wrote:
> >>
> >> Naresh Kamboju writes:
> >> >After this patch applied the reported issue got fixed.
> >>
> >> Great! Thank you Naresh and Michal for helping to get to the bottom of this :-)
> >>
> >> I'll send out a new version tomorrow with the fixes applied and both of you
> >> credited in the changelog for the detection and fix.
> >
> >As we have already found that the usage around memory.{emin, elow} has
> >many limitations, I think memory.{emin, elow} should be used for
> >memcg-tree internally only, that means they can only be used to
> >calculate the protection of a memcg in a specified memcg-tree but
> >should not be exposed to other MM parts.
>
> I agree that the current semantics are mentally taxing and we should generally
> avoid exposing the implementation details outside of memcg where possible. Do
> you have a suggested rework? :-)

Keeping the mem_cgroup_protected() as-is is my suggestion. Anyway I
think it is bad to put memory.{emin, elow} here and there.
If we don't have any better idea by now, just putting all the
references of memory.{emin, elow}  into one
wrapper(mem_cgroup_protected()) is the reasonable solution.

-- 
Thanks
Yafang