Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Wed, 11 Mar 2020 17:18:49 -0700
From:   Minchan Kim <minchan@kernel.org>
To:     Shakeel Butt <shakeelb@google.com>
Cc:     Michal Hocko <mhocko@kernel.org>,
        Dave Hansen <dave.hansen@intel.com>,
        Jann Horn <jannh@google.com>, Linux-MM <linux-mm@kvack.org>,
        kernel list <linux-kernel@vger.kernel.org>,
        Daniel Colascione <dancol@google.com>,
        "Joel Fernandes (Google)" <joel@joelfernandes.org>
Subject: Re: interaction of MADV_PAGEOUT with CoW anonymous mappings?
Message-ID: <20200312001849.GA96953@google.com>
References: <CAG48ez0G3JkMq61gUmyQAaCq=_TwHbi1XKzWRooxZkv08PQKuw@mail.gmail.com>
 <20200310184814.GA8447@dhcp22.suse.cz>
 <CAG48ez2pNSKL9ZTH-PQ93+Kc6ObH6Pa1vVg3OS85WT0TB8m3=A@mail.gmail.com>
 <20200310210906.GD8447@dhcp22.suse.cz>
 <cf95db88-968d-fee5-1c15-10d024c09d8a@intel.com>
 <20200311084513.GD23944@dhcp22.suse.cz>
 <CALvZod6b73_ay_kxph143Aj+XBq04Np0z2bK4Rfn8qppihrmTw@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CALvZod6b73_ay_kxph143Aj+XBq04Np0z2bK4Rfn8qppihrmTw@mail.gmail.com>
User-Agent: Mutt/1.12.2 (2019-09-21)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Wed, Mar 11, 2020 at 04:53:17PM -0700, Shakeel Butt wrote:
> On Wed, Mar 11, 2020 at 1:45 AM Michal Hocko <mhocko@kernel.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?

Maybe, not because process_madvise syscall needs more previliedge(ie,
PTRACE_MODE_ATTACH_FSCREDS) so I guess it would be more secure.
So in that case, I want to rely on the LRU chance for shared pages.

With that, the manager process could give a hint to several processes
and finally makes them paging out.

What do you think?