linux-kernel - Re: [PATCH 2/3] Fix fsync livelock

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Date:	Sun, 5 Oct 2008 15:33:06 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Mikulas Patocka <mpatocka@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, agk@...hat.com, mbroz@...hat.com,
	chris@...chsys.com
Subject: Re: [PATCH 2/3] Fix fsync livelock

On Sun, 5 Oct 2008 18:14:50 -0400 (EDT)
Mikulas Patocka <mpatocka@...hat.com> wrote:

> Fix starvation in memory management.
> 
> The bug happens when one process is doing sequential buffered writes
> to a block device (or file) and another process is attempting to
> execute sync(), fsync() or direct-IO on that device (or file). This
> syncing process will wait indefinitelly, until the first writing
> process finishes.
> 
> For example, run these two commands:
> dd if=/dev/zero of=/dev/sda1 bs=65536 &
> dd if=/dev/sda1 of=/dev/null bs=4096 count=1 iflag=direct
> 
> The bug is caused by sequential walking of address space in
> write_cache_pages and wait_on_page_writeback_range: if some other
> process is constantly making dirty and writeback pages while these
> functions run, the functions will wait on every new page, resulting in
> indefinite wait.

are you sure?
isn't the right fix to just walk the file pages only once?
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