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References: <20231213-zswap-dstmem-v1-0-896763369d04@bytedance.com>
 <20231213-zswap-dstmem-v1-5-896763369d04@bytedance.com> <CAJD7tkb5cKopA-Lfvtsn7sqgqjRf2kyaMwZhhp6SkveNEwArGw@mail.gmail.com>
 <20231214142320.f5cf319e619dbb2127c423e9@linux-foundation.org>
In-Reply-To: <20231214142320.f5cf319e619dbb2127c423e9@linux-foundation.org>
From: Yosry Ahmed <yosryahmed@google.com>
Date: Thu, 14 Dec 2023 14:41:26 -0800
Message-ID: <CAJD7tkaJVB+BoYmcO3MtGD7Ku88Sjk-VAK640h9B-aQzyGPdZQ@mail.gmail.com>
Subject: Re: [PATCH 5/5] mm/zswap: cleanup zswap_reclaim_entry()
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Chengming Zhou <zhouchengming@bytedance.com>, Nhat Pham <nphamcs@gmail.com>, 
	Chris Li <chriscli@google.com>, Johannes Weiner <hannes@cmpxchg.org>, 
	Seth Jennings <sjenning@redhat.com>, Dan Streetman <ddstreet@ieee.org>, 
	Vitaly Wool <vitaly.wool@konsulko.com>, linux-kernel@vger.kernel.org, linux-mm@kvack.org
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On Thu, Dec 14, 2023 at 2:23=E2=80=AFPM Andrew Morton <akpm@linux-foundatio=
n.org> wrote:
>
> On Wed, 13 Dec 2023 17:02:25 -0800 Yosry Ahmed <yosryahmed@google.com> wr=
ote:
>
> > On Tue, Dec 12, 2023 at 8:18=E2=80=AFPM Chengming Zhou
> > <zhouchengming@bytedance.com> wrote:
> > >
> > > Also after the common decompress part goes to __zswap_load(), we can
> > > cleanup the zswap_reclaim_entry() a little.
> >
> > I think you mean zswap_writeback_entry(), same for the commit title.
>
> I updated my copy of the changelog, thanks.
>
> > > -       /*
> > > -        * If we get here because the page is already in swapcache, a
> > > -        * load may be happening concurrently. It is safe and okay to
> > > -        * not free the entry. It is also okay to return !0.
> > > -        */
> >
> > This comment should be moved above the failure check of
> > __read_swap_cache_async() above, not completely removed.
>
> This?

Yes, thanks a lot. Although I think a new version is needed anyway to
address other comments.

>
> --- a/mm/zswap.c~mm-zswap-cleanup-zswap_reclaim_entry-fix
> +++ a/mm/zswap.c
> @@ -1457,8 +1457,14 @@ static int zswap_writeback_entry(struct
>         mpol =3D get_task_policy(current);
>         page =3D __read_swap_cache_async(swpentry, GFP_KERNEL, mpol,
>                                 NO_INTERLEAVE_INDEX, &page_was_allocated,=
 true);
> -       if (!page)
> +       if (!page) {
> +               /*
> +                * If we get here because the page is already in swapcach=
e, a
> +                * load may be happening concurrently. It is safe and oka=
y to
> +                * not free the entry. It is also okay to return !0.
> +                */
>                 return -ENOMEM;
> +       }
>
>         /* Found an existing page, we raced with load/swapin */
>         if (!page_was_allocated) {
>