linux-kernel - Re: [PATCH] Introduce a method to catch mmap_region (was: Recent kernel "mount" slow)

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Message-ID: <20121129063043.GJ4939@ZenIV.linux.org.uk>
Date:	Thu, 29 Nov 2012 06:30:43 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Mikulas Patocka <mpatocka@...hat.com>,
	Jens Axboe <axboe@...nel.dk>,
	Jeff Chua <jeff.chua.linux@...il.com>,
	Lai Jiangshan <laijs@...fujitsu.com>, Jan Kara <jack@...e.cz>,
	lkml <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH] Introduce a method to catch mmap_region (was: Recent
 kernel "mount" slow)

On Thu, Nov 29, 2012 at 06:25:19AM +0000, Al Viro wrote:

> 	Umm...  set_blocksize() is calling kill_bdev(), which does
> truncate_inode_pages(mapping, 0).  What's going to happen to data in
> the dirty pages?  IO in progress is not the only thing to worry about...

Note that sync_blockdev() a few lines prior to that is good only if we
have no other processes doing write(2) (or dirtying the mmapped pages,
for that matter).  The window isn't too wide, but...
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