On Wed, Oct 16, 2013 at 09:18:37AM +0800, Ming Lei wrote:
> Commit 4e7ea81db5(ext4: restructure writeback path) introduces
> another performance regression on random write:
>
> - one more page may be added to ext4 extent in mpage_prepare_extent_to_map,
> and will be submitted for I/O so nr_to_write will become -1 before 'done'
> is set
>
> - the worse thing is that dirty pages may still be retrieved from page
> cache after nr_to_write becomes negative, so lots of small chunks can be
> submitted to block device when page writeback is catching up with write
> path, and performance is hurted.
>
> On one arm A15 board with sata 3.0 SSD(CPU: 1.5GHz dura core, RAM: 2GB,
> SATA controller: 3.0Gbps), this patch can improve below test's result
> from 157MB/sec to 174MB/sec(>10%):
>
> dd if=/dev/zero of=./z.img bs=8K count=512K
>
> The above test is actually prototype of block write in bonnie++ utility.
>
> This patch makes sure no more pages than nr_to_write can be added to extent
> for mapping, so that nr_to_write won't become negative.
>
> Cc: Ted Tso <ty...@mit.edu>
> Cc: linux-e...@vger.kernel.org
> Cc: "linux-fsde...@vger.kernel.org" <linux-fsde...@vger.kernel.org>
> Acked-by: Jan Kara <j...@suse.cz>
> Signed-off-by: Ming Lei <ming....@canonical.com>
Thanks, applied.
- Ted
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