From: Christoph Hellwig <hch@lst.de>
To: Wu Fengguang <fengguang.wu@intel.com>
Cc: Christoph Hellwig <hch@lst.de>, Jan Kara <jack@suse.cz>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH] mm: Avoid livelocking of WB_SYNC_ALL writeback
Date: Sat, 6 Nov 2010 12:45:18 +0100 [thread overview]
Message-ID: <20101106114518.GA1427@lst.de> (raw)
In-Reply-To: <20101106025423.GA14567@localhost>
On Sat, Nov 06, 2010 at 10:54:23AM +0800, Wu Fengguang wrote:
> > I think it would be useful to elaborate here on how livelock avoidance
> > is supposed to work.
>
> It's supposed to sync files in a big loop
>
> for each dirty inode
> write_cache_pages()
> (quickly) tag currently dirty pages
> (maybe slowly) sync all tagged pages
>
> Ideally the loop should call write_cache_pages() _once_ for each inode.
> At least this is the assumption made by commit f446daaea (mm:
> implement writeback livelock avoidance using page tagging).
>
> Setting wbc.nr_to_write to LONG_MAX ensures that writeback_inodes_wb()
> will complete the above loop before returning to wb_writeback(), and
> to prevent wb_writeback() from looping (thus re-syncing extra data) in
> the below range of code.
I know this, but putting a shortened version of this into the comment
would generally be helpful. It should at least mention that the page
tagging is taking care of it.
next prev parent reply other threads:[~2010-11-06 11:45 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-11-05 21:26 [PATCH] mm: Avoid livelocking of WB_SYNC_ALL writeback Jan Kara
2010-11-05 22:30 ` Christoph Hellwig
2010-11-06 2:54 ` Wu Fengguang
2010-11-06 11:45 ` Christoph Hellwig [this message]
2010-11-06 2:55 ` Wu Fengguang
2010-11-06 2:55 ` Wu Fengguang
2010-11-06 16:39 ` Wu Fengguang
2010-11-07 13:34 ` Jan Kara
2010-11-06 1:36 ` Johannes Weiner
2010-11-06 1:36 ` Johannes Weiner
2010-11-07 13:07 ` Jan Kara
2010-11-06 4:12 ` Wu Fengguang
2010-11-06 4:12 ` Wu Fengguang
2010-11-07 13:22 ` Jan Kara
2010-11-07 13:22 ` Jan Kara
2010-11-07 13:37 ` Wu Fengguang
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