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From: Hugh Dickins <hughd@google.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: Dave Chinner <david@fromorbit.com>,
	Michel Lespinasse <walken@google.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Nick Piggin <npiggin@kernel.dk>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Rik van Riel <riel@redhat.com>,
	Kosaki Motohiro <kosaki.motohiro@jp.fujitsu.com>,
	Theodore Tso <tytso@google.com>,
	Michael Rubin <mrubin@google.com>,
	Suleiman Souhlal <suleiman@google.com>
Subject: Re: [PATCH 3/3] mlock: avoid dirtying pages and triggering writeback
Date: Thu, 18 Nov 2010 09:41:22 -0800 (PST)	[thread overview]
Message-ID: <alpine.LSU.2.00.1011180934400.3210@tigran.mtv.corp.google.com> (raw)
In-Reply-To: <20101118133702.GA18834@infradead.org>

On Thu, 18 Nov 2010, Christoph Hellwig wrote:
> On Thu, Nov 18, 2010 at 10:11:43AM +1100, Dave Chinner wrote:
> > Hence I think that avoiding ->page_mkwrite callouts is likely to
> > break some filesystems in subtle, undetected ways.  IMO, regardless
> > of what is done, it would be really good to start by writing a new
> > regression test to exercise and encode the expected the mlock
> > behaviour so we can detect regressions later on....
> 
> I think it would help if we could drink a bit of the test driven design
> coolaid here. Michel, can you write some testcases where pages on a
> shared mapping are mlocked, then dirtied and then munlocked, and then
> written out using msync/fsync.  Anything that fails this test on
> btrfs/ext4/gfs/xfs/etc obviously doesn't work.

Whilst it's hard to argue against a request for testing, Dave's worries
just sprang from a misunderstanding of all the talk about "avoiding ->
page_mkwrite".  There's nothing strange or risky about Michel's patch,
it does not avoid ->page_mkwrite when there is a write: it just stops
pretending that there was a write when locking down the shared area.

Hugh

WARNING: multiple messages have this Message-ID (diff)
From: Hugh Dickins <hughd@google.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: Dave Chinner <david@fromorbit.com>,
	Michel Lespinasse <walken@google.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Nick Piggin <npiggin@kernel.dk>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Rik van Riel <riel@redhat.com>,
	Kosaki Motohiro <kosaki.motohiro@jp.fujitsu.com>,
	Theodore Tso <tytso@google.com>,
	Michael Rubin <mrubin@google.com>,
	Suleiman Souhlal <suleiman@google.com>
Subject: Re: [PATCH 3/3] mlock: avoid dirtying pages and triggering writeback
Date: Thu, 18 Nov 2010 09:41:22 -0800 (PST)	[thread overview]
Message-ID: <alpine.LSU.2.00.1011180934400.3210@tigran.mtv.corp.google.com> (raw)
In-Reply-To: <20101118133702.GA18834@infradead.org>

On Thu, 18 Nov 2010, Christoph Hellwig wrote:
> On Thu, Nov 18, 2010 at 10:11:43AM +1100, Dave Chinner wrote:
> > Hence I think that avoiding ->page_mkwrite callouts is likely to
> > break some filesystems in subtle, undetected ways.  IMO, regardless
> > of what is done, it would be really good to start by writing a new
> > regression test to exercise and encode the expected the mlock
> > behaviour so we can detect regressions later on....
> 
> I think it would help if we could drink a bit of the test driven design
> coolaid here. Michel, can you write some testcases where pages on a
> shared mapping are mlocked, then dirtied and then munlocked, and then
> written out using msync/fsync.  Anything that fails this test on
> btrfs/ext4/gfs/xfs/etc obviously doesn't work.

Whilst it's hard to argue against a request for testing, Dave's worries
just sprang from a misunderstanding of all the talk about "avoiding ->
page_mkwrite".  There's nothing strange or risky about Michel's patch,
it does not avoid ->page_mkwrite when there is a write: it just stops
pretending that there was a write when locking down the shared area.

Hugh

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  reply	other threads:[~2010-11-18 17:41 UTC|newest]

Thread overview: 56+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-11-17 12:23 [PATCH 0/3] Avoid dirtying pages during mlock Michel Lespinasse
2010-11-17 12:23 ` Michel Lespinasse
2010-11-17 12:23 ` [PATCH 1/3] do_wp_page: remove the 'reuse' flag Michel Lespinasse
2010-11-17 12:23   ` Michel Lespinasse
2010-11-17 12:23 ` [PATCH 2/3] do_wp_page: clarify dirty_page handling Michel Lespinasse
2010-11-17 12:23   ` Michel Lespinasse
2010-11-17 12:23 ` [PATCH 3/3] mlock: avoid dirtying pages and triggering writeback Michel Lespinasse
2010-11-17 12:23   ` Michel Lespinasse
2010-11-17 12:57   ` Nick Piggin
2010-11-17 12:57     ` Nick Piggin
2010-11-17 15:28     ` Peter Zijlstra
2010-11-17 15:28       ` Peter Zijlstra
2010-11-17 22:05       ` Michel Lespinasse
2010-11-17 22:05         ` Michel Lespinasse
2010-11-17 22:18         ` Peter Zijlstra
2010-11-17 22:18           ` Peter Zijlstra
2010-11-17 23:11         ` Dave Chinner
2010-11-17 23:11           ` Dave Chinner
2010-11-17 23:31           ` Michel Lespinasse
2010-11-17 23:31             ` Michel Lespinasse
2010-11-19  1:46             ` Dave Chinner
2010-11-19  1:46               ` Dave Chinner
2010-11-17 23:52           ` Ted Ts'o
2010-11-17 23:52             ` Ted Ts'o
2010-11-18  0:53             ` Andrew Morton
2010-11-18  0:53               ` Andrew Morton
2010-11-18 11:03               ` Michel Lespinasse
2010-11-18 11:03                 ` Michel Lespinasse
2010-11-18 13:37           ` Christoph Hellwig
2010-11-18 13:37             ` Christoph Hellwig
2010-11-18 17:41             ` Hugh Dickins [this message]
2010-11-18 17:41               ` Hugh Dickins
2010-11-19  7:23               ` Michel Lespinasse
2010-11-19  7:23                 ` Michel Lespinasse
2010-11-19 13:38                 ` Theodore Tso
2010-11-19 13:42                 ` Theodore Tso
2010-11-19 13:42                   ` Theodore Tso
2010-11-19 15:06                   ` Christoph Hellwig
2010-11-19 15:06                     ` Christoph Hellwig
2010-11-19 22:54                 ` Andrew Morton
2010-11-19 22:54                   ` Andrew Morton
2010-11-19 23:22                   ` Ted Ts'o
2010-11-19 23:22                     ` Ted Ts'o
2010-11-20  0:29                     ` Dustin Kirkland
2010-11-19 23:31                   ` Michel Lespinasse
2010-11-19 23:31                     ` Michel Lespinasse
2010-11-19 23:54                 ` Dave Chinner
2010-11-19 23:54                   ` Dave Chinner
2010-11-18  5:46       ` Nick Piggin
2010-11-18  5:46         ` Nick Piggin
2010-11-18 10:43         ` Theodore Tso
2010-11-18 10:43           ` Theodore Tso
2010-11-18 13:39           ` Christoph Hellwig
2010-11-18 13:39             ` Christoph Hellwig
2010-11-18 18:00             ` Hugh Dickins
2010-11-18 18:00               ` Hugh Dickins

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