* [PATCH] writeback: write_cache_pages doesn't terminate at nr_to_write <= 0
@ 2010-08-23 4:43 Dave Chinner
2010-08-23 8:27 ` Wu Fengguang
2010-08-23 13:25 ` Christoph Hellwig
0 siblings, 2 replies; 3+ messages in thread
From: Dave Chinner @ 2010-08-23 4:43 UTC (permalink / raw)
To: linux-kernel; +Cc: linux-fsdevel, xfs
From: Dave Chinner <dchinner@redhat.com>
I noticed XFS writeback in 2.6.36-rc1 was much slower than it should have
been. Enabling writeback tracing showed:
flush-253:16-8516 [007] 1342952.351608: wbc_writepage: bdi 253:16: towrt=1024 skip=0 mode=0 kupd=0 bgrd=1 reclm=0 cyclic=1 more=0 older=0x0 start=0x0 end=0x0
flush-253:16-8516 [007] 1342952.351654: wbc_writepage: bdi 253:16: towrt=1023 skip=0 mode=0 kupd=0 bgrd=1 reclm=0 cyclic=1 more=0 older=0x0 start=0x0 end=0x0
flush-253:16-8516 [000] 1342952.369520: wbc_writepage: bdi 253:16: towrt=0 skip=0 mode=0 kupd=0 bgrd=1 reclm=0 cyclic=1 more=0 older=0x0 start=0x0 end=0x0
flush-253:16-8516 [000] 1342952.369542: wbc_writepage: bdi 253:16: towrt=-1 skip=0 mode=0 kupd=0 bgrd=1 reclm=0 cyclic=1 more=0 older=0x0 start=0x0 end=0x0
flush-253:16-8516 [000] 1342952.369549: wbc_writepage: bdi 253:16: towrt=-2 skip=0 mode=0 kupd=0 bgrd=1 reclm=0 cyclic=1 more=0 older=0x0 start=0x0 end=0x0
Writeback is not terminating in background writeback if ->writepage is
returning with wbc->nr_to_write == 0, resulting in sub-optimal single page
writeback on XFS.
Fix the write_cache_pages loop to terminate correctly when this situation
occurs and so prevent this sub-optimal background writeback pattern. This
improves sustained sequential buffered write performance from around
250MB/s to 750MB/s for a 100GB file on an XFS filesystem on my 8p test VM.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
mm/page-writeback.c | 26 ++++++++++----------------
1 files changed, 10 insertions(+), 16 deletions(-)
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 7262aac..f069782 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -984,22 +984,16 @@ continue_unlock:
}
}
- if (wbc->nr_to_write > 0) {
- if (--wbc->nr_to_write == 0 &&
- wbc->sync_mode == WB_SYNC_NONE) {
- /*
- * We stop writing back only if we are
- * not doing integrity sync. In case of
- * integrity sync we have to keep going
- * because someone may be concurrently
- * dirtying pages, and we might have
- * synced a lot of newly appeared dirty
- * pages, but have not synced all of the
- * old dirty pages.
- */
- done = 1;
- break;
- }
+ /*
+ * We stop writing back only if we are not doing
+ * integrity sync. In case of integrity sync we have to
+ * keep going until we have written all the pages
+ * we tagged for writeback prior to entering this loop.
+ */
+ if (--wbc->nr_to_write <= 0 &&
+ wbc->sync_mode == WB_SYNC_NONE) {
+ done = 1;
+ break;
}
}
pagevec_release(&pvec);
--
1.7.1
^ permalink raw reply related [flat|nested] 3+ messages in thread* Re: [PATCH] writeback: write_cache_pages doesn't terminate at nr_to_write <= 0
2010-08-23 4:43 [PATCH] writeback: write_cache_pages doesn't terminate at nr_to_write <= 0 Dave Chinner
@ 2010-08-23 8:27 ` Wu Fengguang
2010-08-23 13:25 ` Christoph Hellwig
1 sibling, 0 replies; 3+ messages in thread
From: Wu Fengguang @ 2010-08-23 8:27 UTC (permalink / raw)
To: Dave Chinner; +Cc: linux-kernel, linux-fsdevel, xfs, Andrew Morton
On Mon, Aug 23, 2010 at 02:43:40PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> I noticed XFS writeback in 2.6.36-rc1 was much slower than it should have
> been. Enabling writeback tracing showed:
>
> flush-253:16-8516 [007] 1342952.351608: wbc_writepage: bdi 253:16: towrt=1024 skip=0 mode=0 kupd=0 bgrd=1 reclm=0 cyclic=1 more=0 older=0x0 start=0x0 end=0x0
> flush-253:16-8516 [007] 1342952.351654: wbc_writepage: bdi 253:16: towrt=1023 skip=0 mode=0 kupd=0 bgrd=1 reclm=0 cyclic=1 more=0 older=0x0 start=0x0 end=0x0
> flush-253:16-8516 [000] 1342952.369520: wbc_writepage: bdi 253:16: towrt=0 skip=0 mode=0 kupd=0 bgrd=1 reclm=0 cyclic=1 more=0 older=0x0 start=0x0 end=0x0
> flush-253:16-8516 [000] 1342952.369542: wbc_writepage: bdi 253:16: towrt=-1 skip=0 mode=0 kupd=0 bgrd=1 reclm=0 cyclic=1 more=0 older=0x0 start=0x0 end=0x0
> flush-253:16-8516 [000] 1342952.369549: wbc_writepage: bdi 253:16: towrt=-2 skip=0 mode=0 kupd=0 bgrd=1 reclm=0 cyclic=1 more=0 older=0x0 start=0x0 end=0x0
>
> Writeback is not terminating in background writeback if ->writepage is
> returning with wbc->nr_to_write == 0, resulting in sub-optimal single page
> writeback on XFS.
The new code looks more simple, and more robust in case ->writepage
modifies wbc->nr_to_write (as in xfs_vm_writepage).
Reviewed-by: Wu Fengguang <fengguang.wu@intel.com>
Thanks,
Fengguang
> Fix the write_cache_pages loop to terminate correctly when this situation
> occurs and so prevent this sub-optimal background writeback pattern. This
> improves sustained sequential buffered write performance from around
> 250MB/s to 750MB/s for a 100GB file on an XFS filesystem on my 8p test VM.
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
> mm/page-writeback.c | 26 ++++++++++----------------
> 1 files changed, 10 insertions(+), 16 deletions(-)
>
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 7262aac..f069782 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -984,22 +984,16 @@ continue_unlock:
> }
> }
>
> - if (wbc->nr_to_write > 0) {
> - if (--wbc->nr_to_write == 0 &&
> - wbc->sync_mode == WB_SYNC_NONE) {
> - /*
> - * We stop writing back only if we are
> - * not doing integrity sync. In case of
> - * integrity sync we have to keep going
> - * because someone may be concurrently
> - * dirtying pages, and we might have
> - * synced a lot of newly appeared dirty
> - * pages, but have not synced all of the
> - * old dirty pages.
> - */
> - done = 1;
> - break;
> - }
> + /*
> + * We stop writing back only if we are not doing
> + * integrity sync. In case of integrity sync we have to
> + * keep going until we have written all the pages
> + * we tagged for writeback prior to entering this loop.
> + */
> + if (--wbc->nr_to_write <= 0 &&
> + wbc->sync_mode == WB_SYNC_NONE) {
> + done = 1;
> + break;
> }
> }
> pagevec_release(&pvec);
> --
> 1.7.1
>
> --
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^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH] writeback: write_cache_pages doesn't terminate at nr_to_write <= 0
2010-08-23 4:43 [PATCH] writeback: write_cache_pages doesn't terminate at nr_to_write <= 0 Dave Chinner
2010-08-23 8:27 ` Wu Fengguang
@ 2010-08-23 13:25 ` Christoph Hellwig
1 sibling, 0 replies; 3+ messages in thread
From: Christoph Hellwig @ 2010-08-23 13:25 UTC (permalink / raw)
To: Dave Chinner; +Cc: linux-kernel, linux-fsdevel, xfs
Looks good,
Reviewed-by: Christoph Hellwig <hch@lst.de>
^ permalink raw reply [flat|nested] 3+ messages in thread
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2010-08-23 4:43 [PATCH] writeback: write_cache_pages doesn't terminate at nr_to_write <= 0 Dave Chinner
2010-08-23 8:27 ` Wu Fengguang
2010-08-23 13:25 ` Christoph Hellwig
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