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Sender: Minchan Kim <minchan.kim@gmail.com>
Date:   Thu, 18 Mar 2021 08:19:12 -0700
From:   Minchan Kim <minchan@kernel.org>
To:     Shakeel Butt <shakeelb@google.com>
Cc:     Heiko Carstens <hca@linux.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Roman Gushchin <guro@fb.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
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        Vasily Gorbik <gor@linux.ibm.com>,
        Linux MM <linux-mm@kvack.org>,
        Linux-Next Mailing List <linux-next@vger.kernel.org>
Subject: Re: [BUG -next] "memcg: charge before adding to swapcache on swapin"
 broken
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On Wed, Mar 17, 2021 at 06:49:27PM -0700, Shakeel Butt wrote:
> On Wed, Mar 17, 2021 at 6:31 PM Minchan Kim <minchan@kernel.org> wrote:
> >
> [...]
> > >
> > > The simplest solution I can think of is to do set_page_private(page,
> > > entry.val) before swap_readpage(page, true) and set_page_private(page,
> > > 0) after.
> >
> > Since I did't read the bug in detail, I couldn't come up with how the
> > missing reset is connected the problem while missing set_page_private
> > with entry.val is clear.
> 
> This particular bug is about missing set_page_private(page,
> entry.val). I was wondering if we should always reset page->private or
> just leave it as is? I think it is safer to reset.

For safeness point of view, I couldn't find something wrong since
page_private will be used once the page turns out PageSwapCache.
(please chime in if someone found)

Having said, I agree it would be more consistent and safer.