linux-kernel - Re: ftruncate-mmap: pages are lost after writing to mmaped file.

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Date:	Wed, 18 Mar 2009 16:54:33 -0700
From:	Ying Han <yinghan@...gle.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>, guichaz@...il.com,
	Alex Khesin <alexk@...gle.com>,
	Mike Waychison <mikew@...gle.com>,
	Rohit Seth <rohitseth@...gle.com>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: ftruncate-mmap: pages are lost after writing to mmaped file.

On Wed, Mar 18, 2009 at 4:36 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
>
> On Wed, 18 Mar 2009, Ying Han wrote:
>> >
>> > Can you say what filesystem, and what mount-flags you use? Iirc, last time
>> > we had MAP_SHARED lost writes it was at least partly triggered by the
>> > filesystem doing its own flushing independently of the VM (ie ext3 with
>> > "data=journal", I think), so that kind of thing does tend to matter.
>>
>> /etc/fstab
>> "/dev/hda1 / ext2 defaults 1 0"
>
> Sadly, /etc/fstab is not necessarily accurate for the root filesystem. At
> least Fedora will ignore the flags in it.
>
> What does /proc/mounts say? That should be a more reliable indication of
> what the kernel actually does.

"/dev/root / ext2 rw,errors=continue 0 0"

>
> That said, I assume the ext2 part is accurate. Maybe that's why people
> haven't seen it - I guess most testing was done on ext3. It certainly was
> for me.
>
>> > Ying Han - since you're all set up for testing this and have reproduced it
>> > on multiple kernels, can you try it on a few more kernel versions? It
>> > would be interesting to both go further back in time (say 2.6.15-ish),
>> > _and_ check something like 2.6.21 which had the exact dirty accounting
>> > fix. Maybe it's not really an old bug - maybe we re-introduced a bug that
>> > was fixed for a while.
>>
>> I will give a try.
>
> Thanks,
>
>                Linus
>
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