linux-kernel - Re: interaction of MADV_PAGEOUT with CoW anonymous mappings?

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Date:   Wed, 11 Mar 2020 09:45:13 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Dave Hansen <dave.hansen@...el.com>,
        Minchan Kim <minchan@...nel.org>
Cc:     Jann Horn <jannh@...gle.com>, Linux-MM <linux-mm@...ck.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        Daniel Colascione <dancol@...gle.com>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>
Subject: Re: interaction of MADV_PAGEOUT with CoW anonymous mappings?

On Tue 10-03-20 15:48:31, Dave Hansen wrote:
> Maybe instead of just punting on MADV_PAGEOUT for map_count>1 we should
> only let it affect the *local* process.  We could still put the page in
> the swap cache, we just wouldn't go do the rmap walk.

Is it really worth medling with the reclaim code and special case
MADV_PAGEOUT there? I mean it is quite reasonable to have an initial
implementation that doesn't really touch shared pages because that can
lead to all sorts of hard to debug and unexpected problems. So I would
much rather go with a simple patch to check map count first and see
whether somebody actually cares about those shared pages and go from
there.

Minchan, do you want to take my diff and turn it into the proper patch
or should I do it.

-- 
Michal Hocko
SUSE Labs