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From:   Brian Geffon <bgeffon@google.com>
Date:   Mon, 3 Oct 2022 10:46:43 -0400
Message-ID: <CADyq12wo_LS3v44Fs4R68hZAcmM4YVZ=17Vfyo+SECX15Y9LXg@mail.gmail.com>
Subject: Re: [PATCH] zram: Always expose rw_page
To:     Sergey Senozhatsky <senozhatsky@chromium.org>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Minchan Kim <minchan@kernel.org>,
        Nitin Gupta <ngupta@vflare.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Suleiman Souhlal <suleiman@google.com>,
        Rom Lemarchand <romlem@google.com>,
        linux-mm <linux-mm@kvack.org>
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On Sun, Oct 2, 2022 at 10:59 PM Sergey Senozhatsky
<senozhatsky@chromium.org> wrote:
>
> On (22/09/30 15:52), Brian Geffon wrote:
> > Currently zram will adjust its fops to a version which does not
> > contain rw_page when a backing device has been assigned. This is
> > done to prevent upper layers from assuming a synchronous operation
> > when a page may have been written back. This forces every operation
> > through bio which has overhead associated with bio_alloc/frees.
> >
> > The code can be simplified to always expose a rw_page method and
> > only in the rare event that a page is written back we instead will
> > return -EOPNOTSUPP forcing the upper layer to fallback to bio.
>
> Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>

Thank you.

>
> > @@ -1267,6 +1253,9 @@ static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
> >               struct bio_vec bvec;
> >
> >               zram_slot_unlock(zram, index);
> > +             /* If we don't have a bio we came via rw_page, we must fallback to bio */
> > +             if (!bio)
> > +                     return -EOPNOTSUPP;
>
> The comment is above 80 cols.

Fixed in a new patch.