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Date:   Thu, 18 Mar 2021 16:08:19 +0100
From:   Michal Hocko <mhocko@suse.com>
To:     Johannes Weiner <hannes@cmpxchg.org>
Cc:     Shakeel Butt <shakeelb@google.com>,
        Hugh Dickins <hughd@google.com>, Roman Gushchin <guro@fb.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Minchan Kim <minchan@kernel.org>, cgroups@vger.kernel.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Heiko Carstens <hca@linux.ibm.com>
Subject: Re: [PATCH] memcg: set page->private before calling swap_readpage
Message-ID: <YFNs46Yd6pOwotSt@dhcp22.suse.cz>
References: <20210318015959.2986837-1-shakeelb@google.com>
 <YFNdNeczjnmF55bm@dhcp22.suse.cz>
 <YFNreYne/27T9XA8@cmpxchg.org>
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On Thu 18-03-21 11:02:17, Johannes Weiner wrote:
> On Thu, Mar 18, 2021 at 03:01:25PM +0100, Michal Hocko wrote:
> > On Wed 17-03-21 18:59:59, Shakeel Butt wrote:
> > > The function swap_readpage() (and other functions it call) extracts swap
> > > entry from page->private. However for SWP_SYNCHRONOUS_IO, the kernel
> > > skips the swapcache and thus we need to manually set the page->private
> > > with the swap entry before calling swap_readpage().
> > 
> > One thing that is not really clear to me is whether/why this is only
> > needed with your patch. Can you expand a bit on that please? Maybe I am
> > just missing something obvious but I just do not see any connection.
> 
> It was always needed, his original patch erroneously removed it.

Ahh, I can see it now. I must have been blind. Thanks!

-- 
Michal Hocko
SUSE Labs