linux-kernel - Re: [PATCH] memcontrol: only transfer the memcg data for migration

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Message-ID: <CAJD7tkY=_32gFQP0S3me+N_qDPv4MykQ8Tmczsb6ewJSs2hsbg@mail.gmail.com>
Date:   Tue, 3 Oct 2023 16:54:14 -0700
From:   Yosry Ahmed <yosryahmed@...gle.com>
To:     Nhat Pham <nphamcs@...il.com>
Cc:     akpm@...ux-foundation.org, riel@...riel.com, hannes@...xchg.org,
        mhocko@...nel.org, roman.gushchin@...ux.dev, shakeelb@...gle.com,
        muchun.song@...ux.dev, tj@...nel.org, lizefan.x@...edance.com,
        shuah@...nel.org, mike.kravetz@...cle.com, fvdl@...gle.com,
        linux-mm@...ck.org, kernel-team@...a.com,
        linux-kernel@...r.kernel.org, cgroups@...r.kernel.org
Subject: Re: [PATCH] memcontrol: only transfer the memcg data for migration

On Tue, Oct 3, 2023 at 4:31 PM Nhat Pham <nphamcs@...il.com> wrote:
>
> On Tue, Oct 3, 2023 at 4:22 PM Yosry Ahmed <yosryahmed@...gle.com> wrote:
> >
> > On Tue, Oct 3, 2023 at 4:14 PM Nhat Pham <nphamcs@...il.com> wrote:
> > >
> > > For most migration use cases, only transfer the memcg data from the old
> > > folio to the new folio, and clear the old folio's memcg data. No
> > > charging and uncharging will be done. These use cases include the new
> > > hugetlb memcg accounting behavior (which was not previously handled).
> > >
> > > This shaves off some work on the migration path, and avoids the
> > > temporary double charging of a folio during its migration.
> > >
> > > The only exception is replace_page_cache_folio(), which will use the old
> > > mem_cgroup_migrate() (now renamed to mem_cgroup_replace_folio). In that
> > > context, the isolation of the old page isn't quite as thorough as with
> > > migration, so we cannot use our new implementation directly.
> > >
> > > This patch is the result of the following discussion on the new hugetlb
> > > memcg accounting behavior:
> > >
> > > https://lore.kernel.org/lkml/20231003171329.GB314430@monkey/
> > >
> > > Reported-by: Mike Kravetz <mike.kravetz@...cle.com>
> > > Closes: https://lore.kernel.org/lkml/20231003171329.GB314430@monkey/
> > > Suggested-by: Johannes Weiner <hannes@...xchg.org>
> > > Signed-off-by: Nhat Pham <nphamcs@...il.com>
> >
> > Does this patch fit before or after your series? In both cases I think
> > there might be a problem for bisectability.
>
> Hmm my intention for this patch is as a fixlet.
> (i.e it should be eventually squashed to the second patch of that series).
> I just include the extra context on the fixlet for review purposes.
>
> My apologies - should have been much clearer.
> (Perhaps I should just send out v4 at this point?)
>

It's really up to Andrew, just make it clear what the intention is.

Thanks!