> 2) the flusher thread is not woken up because we test writeback_in_progress()
> in balance_dirty_pages().
>
> if (unlikely(!writeback_in_progress(bdi)))
> bdi_start_background_writeback(bdi);
>
[...]
> This should be fixable by removing the BDI_writeback_running flag
> before doing the wait sleep.
I tried adding the below patch, and this time it shows 1.8%
performance improvement. Looks not bad :-)
3.1.0-rc8-ioless6a+ 3.1.0-rc8-ioless6-requeue7+
------------------------ ------------------------
32.09 +1.1% 32.45 thresh=1M/ext4-10dd-4k-8p-4096M-1M:10-X
51.36 +3.2% 53.00 thresh=1M/ext4-1dd-4k-8p-4096M-1M:10-X
46.93 +1.9% 47.80 thresh=1M/ext4-2dd-4k-8p-4096M-1M:10-X
28.68 +1.6% 29.15 thresh=1M/xfs-10dd-4k-8p-4096M-1M:10-X
51.95 +4.2% 54.13 thresh=1M/xfs-1dd-4k-8p-4096M-1M:10-X
47.07 +1.5% 47.80 thresh=1M/xfs-2dd-4k-8p-4096M-1M:10-X
54.37 +2.2% 55.58 thresh=8M/btrfs-10dd-4k-8p-4096M-8M:10-X
56.12 +4.2% 58.49 thresh=8M/btrfs-1dd-4k-8p-4096M-8M:10-X
56.22 +2.4% 57.55 thresh=8M/btrfs-2dd-4k-8p-4096M-8M:10-X
32.21 +1.7% 32.77 thresh=8M/ext3-10dd-4k-8p-4096M-8M:10-X
45.37 +2.7% 46.58 thresh=8M/ext3-1dd-4k-8p-4096M-8M:10-X
43.71 +2.6% 44.83 thresh=8M/ext3-2dd-4k-8p-4096M-8M:10-X
35.58 +1.3% 36.06 thresh=8M/ext4-10dd-4k-8p-4096M-8M:10-X
56.39 +0.4% 56.61 thresh=8M/ext4-1dd-4k-8p-4096M-8M:10-X
51.26 +1.4% 51.98 thresh=8M/ext4-2dd-4k-8p-4096M-8M:10-X
31.07 +0.3% 31.16 thresh=8M/xfs-10dd-4k-8p-4096M-8M:10-X
55.44 -2.0% 54.33 thresh=8M/xfs-1dd-4k-8p-4096M-8M:10-X
47.59 +0.6% 47.87 thresh=8M/xfs-2dd-4k-8p-4096M-8M:10-X
823.40 +1.8% 838.14 TOTAL
--- linux-next.orig/fs/fs-writeback.c 2011-10-15 08:30:48.000000000 +0800
+++ linux-next/fs/fs-writeback.c 2011-10-15 08:31:36.000000000 +0800
@@ -809,8 +809,10 @@ static long wb_writeback(struct bdi_writ
break;
trace_writeback_wait(wb->bdi, work);
spin_unlock(&wb->list_lock);
+ clear_bit(BDI_writeback_running, &wb->bdi->state);
__set_current_state(TASK_INTERRUPTIBLE);
schedule_timeout(pause);
+ set_bit(BDI_writeback_running, &wb->bdi->state);
if (pause < max_pause)
pause <<= 1;
spin_lock(&wb->list_lock);
--
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