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From: Minchan Kim <minchan@kernel.org>
To: Michal Hocko <mhocko@kernel.org>
Cc: Jann Horn <jannh@google.com>, Linux-MM <linux-mm@kvack.org>,
	kernel list <linux-kernel@vger.kernel.org>,
	Daniel Colascione <dancol@google.com>,
	Dave Hansen <dave.hansen@intel.com>,
	"Joel Fernandes (Google)" <joel@joelfernandes.org>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: interaction of MADV_PAGEOUT with CoW anonymous mappings?
Date: Tue, 17 Mar 2020 10:20:22 -0700
Message-ID: <20200317172022.GD73302@google.com> (raw)
In-Reply-To: <20200317155855.GS26018@dhcp22.suse.cz>

On Tue, Mar 17, 2020 at 04:58:55PM +0100, Michal Hocko wrote:
> On Tue 17-03-20 08:00:55, Minchan Kim wrote:
> > On Tue, Mar 17, 2020 at 08:12:39AM +0100, Michal Hocko wrote:
> [...]
> > > Just to make it clear, are you really suggesting to special case
> > > page_check_references for madvise path?
> > > 
> > 
> > No, (page_mapcount() >  1) checks *effectively* fixes the performance
> > bug as well as vulnerability issue.
> 
> Ahh, ok then we are on the same page. You were replying to the part
> where I have pointed out that you can control aging by these calls
> and your response suggested that this is somehow undesirable behavior or
> even a bug.

Sorry about the confusing.

I want to clarify my speaking.

If we don't have vulnerability issue Jann raised, the performance issue
Daniel pointed should be fixed by introducing a special flag in
page_check_references from madvise path to avoid cleaning of access bit
from other processes's pte. With it, we don't need to limit semantic of
MADV_PAGEOUT as "exclusive page only" so that MADV_PAGEOUT will work
*cold* shared pages as well as exclusive one.

However, since we have the vulnerability issue, *unfortunately*, we need
to make MADV_PAGEOUT's semantic working with only exclusive page. 
Thus, page_mapcount check in madvise patch will fix both issues
*effectively*.

Thanks.


  reply index

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-10 18:08 Jann Horn
2020-03-10 18:48 ` Michal Hocko
2020-03-10 19:11   ` Jann Horn
2020-03-10 21:09     ` Michal Hocko
2020-03-10 22:48       ` Dave Hansen
2020-03-11  8:45         ` Michal Hocko
2020-03-11 22:02           ` Minchan Kim
2020-03-11 23:53           ` Shakeel Butt
2020-03-12  0:18             ` Minchan Kim
2020-03-12  2:03               ` Daniel Colascione
2020-03-12 15:15                 ` Shakeel Butt
2020-03-10 20:19   ` Daniel Colascione
2020-03-10 21:40     ` Jann Horn
2020-03-10 21:52       ` Daniel Colascione
2020-03-10 22:14 ` Minchan Kim
2020-03-12  8:22 ` Michal Hocko
2020-03-12 15:40   ` Vlastimil Babka
2020-03-12 20:16   ` Minchan Kim
2020-03-12 20:26     ` Dave Hansen
2020-03-12 20:41     ` Michal Hocko
2020-03-13  2:08       ` Minchan Kim
2020-03-13  8:05         ` Michal Hocko
2020-03-13 20:59           ` Minchan Kim
2020-03-16  9:20             ` Michal Hocko
2020-03-17  1:43               ` Minchan Kim
2020-03-17  7:12                 ` Michal Hocko
2020-03-17 15:00                   ` Minchan Kim
2020-03-17 15:58                     ` Michal Hocko
2020-03-17 17:20                       ` Minchan Kim [this message]
2020-03-12 21:41     ` Dave Hansen
2020-03-13  2:00       ` Minchan Kim
2020-03-13 16:59         ` Dave Hansen
2020-03-13 21:13           ` Minchan Kim
2020-03-12 23:29     ` Jann Horn

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