linux-kernel - Re: [PATCH 01/17] writeback: introduce .tagged_sync for the WB_SYNC

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Message-ID: <20110512224013.GH19446@dastard>
Date:	Fri, 13 May 2011 08:40:13 +1000
From:	Dave Chinner <david@...morbit.com>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, Jan Kara <jack@...e.cz>,
	Christoph Hellwig <hch@...radead.org>,
	linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 01/17] writeback: introduce .tagged_sync for the
 WB_SYNC_NONE sync stage

On Thu, May 12, 2011 at 09:57:07PM +0800, Wu Fengguang wrote:
> sync(2) is performed in two stages: the WB_SYNC_NONE sync and the
> WB_SYNC_ALL sync. Tag the first stage with wbc.tagged_sync and do
> livelock prevention for it, too.
> 
> Note that writeback_inodes_sb() is called by not only sync(), they are
> treated the same because the other callers also need livelock prevention.
> 
> Impact:  It changes the order in which pages/inodes are synced to disk.
> Now in the WB_SYNC_NONE stage, it won't proceed to write the next inode
> until finished with the current inode.

What about all the filesystems that implement their own
.writepages()/write_cache_pages() functions or have
have special code that checks WB_SYNC_ALL in .writepages (e.g. gfs2,
ext4, btrfs and perhaps others). Don't they all need to be aware of
this tagged_sync field?

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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