linux-kernel - Re: [PATCH] memcg: set page->private before calling swap

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Date:   Thu, 18 Mar 2021 11:02:17 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Shakeel Butt <shakeelb@...gle.com>,
        Hugh Dickins <hughd@...gle.com>, Roman Gushchin <guro@...com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Minchan Kim <minchan@...nel.org>, cgroups@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Heiko Carstens <hca@...ux.ibm.com>
Subject: Re: [PATCH] memcg: set page->private before calling swap_readpage

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.