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From:   Brian Geffon <bgeffon@google.com>
Date:   Wed, 10 Aug 2022 15:18:54 -0400
Message-ID: <CADyq12wAUyo4=Wya4zvD6RiVdqcwwcMqZ3xEDa1k6jVY0_o_jg@mail.gmail.com>
Subject: Re: [RFC PATCH 1/1] zram: Allow rw_page when page isn't written back.
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>,
        linux-mm <linux-mm@kvack.org>
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Thanks Sergey,

On Mon, Aug 8, 2022 at 9:38 PM Sergey Senozhatsky
<senozhatsky@chromium.org> wrote:
>
> On (22/08/08 12:50), Brian Geffon wrote:
> [..]
> >
> >       pr_info("setup backing device %s\n", file_name);
> > @@ -722,7 +707,8 @@ static ssize_t writeback_store(struct device *dev,
> >
> >               if (zram_test_flag(zram, index, ZRAM_WB) ||
> >                               zram_test_flag(zram, index, ZRAM_SAME) ||
> > -                             zram_test_flag(zram, index, ZRAM_UNDER_WB))
> > +                             zram_test_flag(zram, index, ZRAM_UNDER_WB) ||
> > +                             zram_test_flag(zram, index, ZRAM_NO_WB))
> >                       goto next;
>
> mark_idle() probably should also test ZRAM_NO_WB bit.

While we definitely can add that check in mark_idle() it actually
doesn't hurt to allow marking the page as idle as NO_WB only controls
the writeback aspect and as long as the page is marked NO_WB it won't
be written back, idle or not. Definitely happy to add it in later
versions if people like this approach in general.