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

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Message-ID: <CALvZod6b73_ay_kxph143Aj+XBq04Np0z2bK4Rfn8qppihrmTw@mail.gmail.com>
Date:   Wed, 11 Mar 2020 16:53:17 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Minchan Kim <minchan@...nel.org>, 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 Wed, Mar 11, 2020 at 1:45 AM Michal Hocko <mhocko@...nel.org> wrote:
>
> 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.
>

What about the remote_madvise(MADV_PAGEOUT)? Will your patch disable
the pageout from that code path as well for pages with mapcount > 1?