linux-kernel - Re: [PATCH v2 1/4] mm/filemap: Add folio_lock

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Date:   Tue, 25 Apr 2023 07:19:48 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Hillf Danton <hdanton@...a.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Yu Zhao <yuzhao@...gle.com>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v2 1/4] mm/filemap: Add folio_lock_timeout()

Hi,

On Mon, Apr 24, 2023 at 6:09 PM Hillf Danton <hdanton@...a.com> wrote:
>
> On 24 Apr 2023 09:56:58 -0700 Douglas Anderson <dianders@...omium.org>
> > On Fri, Apr 21, 2023 at 10:19=E2=80=AFPM Hillf Danton <hdanton@...a.com> wrote:
> > > If kcompactd is waken
> > > up by kswapd, waiting for slow IO is the right thing to do.
> >
> > I don't have enough intuition here, so I'm happy to take others'
> > advice here. I guess my thought was that kcompactd is explicitly not
> > using the full "sync" and instead choosing the "sync light". To me
> > that means we shouldn't block for _too_ long.
>
> Take a look at another case of lock wait [1].
>
> [1] https://lore.kernel.org/lkml/CAHk-=wgyL9OujQ72er7oXt_VsMeno4bMKCTydBT1WSaagZ_5CA@mail.gmail.com/

So is this an explicit NAK on this approach, then? It still feels
worthwhile to me given the current kcompactd design where there is a
single thread that's in charge of going through and cleaning up all of
memory. Any single pags isn't _that_ important for kcompactd to deal
with and it's nice not to block the whole task's ability to make
progress. kcompactd is already very much designed in this model (which
is why SYNC_LIGHT exists in the first place) and that's why my patch
series was relatively simple/short. That being said, if people really
don't think I should pursue this then I won't send another version and
we can drop it.

-Doug