linux-kernel - Re: [PATCH v2] mm: zswap: increase reject_compress_poor but not reject_compress

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Message-ID: <CAJD7tkbHrMzi0z0SzQJj32cDrx4tyH5=_o41GM6JGf9DjahkYg@mail.gmail.com>
Date: Sat, 17 Feb 2024 15:14:34 -0800
From: Yosry Ahmed <yosryahmed@...gle.com>
To: Barry Song <21cnbao@...il.com>
Cc: akpm@...ux-foundation.org, hannes@...xchg.org, linux-mm@...ck.org, 
	nphamcs@...il.com, zhouchengming@...edance.com, senozhatsky@...omium.org, 
	linux-kernel@...r.kernel.org, Barry Song <v-songbaohua@...o.com>
Subject: Re: [PATCH v2] mm: zswap: increase reject_compress_poor but not
 reject_compress_fail if compression returns ENOSPC

On Sat, Feb 17, 2024 at 2:19 AM Barry Song <21cnbao@...il.com> wrote:
>
> On Sat, Feb 17, 2024 at 4:57 PM Yosry Ahmed <yosryahmed@...gle.com> wrote:
> >
> > On Sat, Feb 17, 2024 at 06:36:42PM +1300, Barry Song wrote:
> > > From: Barry Song <v-songbaohua@...o.com>
> > >
> > > We used to rely on the returned -ENOSPC of zpool_malloc() to increase
> > > reject_compress_poor. But the code wouldn't get to there after commit
> > > 744e1885922a ("crypto: scomp - fix req->dst buffer overflow") as the
> > > new code will goto out immediately after the special compression case
> > > happens. So there might be no longer a chance to execute zpool_malloc
> > > now. We are incorrectly increasing zswap_reject_compress_fail instead.
> > > Thus, we need to fix the counters handling right after compressions
> > > return ENOSPC. This patch also centralizes the counters handling for
> > > all of compress_poor, compress_fail and alloc_fail.
> > >
> > > Fixes: 744e1885922a ("crypto: scomp - fix req->dst buffer overflow")
> > > Cc: Chengming Zhou <zhouchengming@...edance.com>
> > > Cc: Nhat Pham <nphamcs@...il.com>
> > > Cc: Sergey Senozhatsky <senozhatsky@...omium.org>
> > > Signed-off-by: Barry Song <v-songbaohua@...o.com>
> > > ---
> > >  -v2:
> > >  * correct the fixes target according to Yosry, Chengming, Nhat's
> > >    comments;
> > >  * centralize the counters handling according to Yosry's comment
> >
> > Yet Yosry is not CC'd :P
>
> terribly sorry. I thought you were in my git send-email list ... but you
> were not...

No problem, I caught it on linux-mm anyway :)

>
> >
> > The patch LGTM, but it won't apply on top of mm-unstable given the
> > amount of zswap refactoring there. I would rebase on top of mm-unstable
> > if I were you (and if you did, add mm-unstable in the subject prefix).
>
> This patch has a "fixes" tag, so I assume it should be also in 6.8?

Hmm that's up to Andrew. This fixes debug counters so it's not
critical. On the other hand, it will conflict with the cleanup series
in his tree and he'll have to rebase and fix the conflicts (which
aren't a lot, but could still be annoying). Personally I think this
can wait till v6.9, but if Andrew doesn't have a problem taking it for
v6.8 that's fine too.