Btrfs: avoid unnecessary ordered extent cache resets
After an ordered extent completes, don't blindly reset the
inode's ordered tree last accessed ordered extent pointer.
While running the xfstests I noticed that about 29% of the
time the ordered extent to which tree->last pointed was not
the same as our just completed ordered extent. After that I
ran the following sysbench test (after a prepare phase) and
noticed that about 68% of the time tree->last pointed to
a different ordered extent too.
sysbench --test=fileio --file-num=32 --file-total-size=4G \
--file-test-mode=rndwr --num-threads=512 \
--file-block-size=32768 --max-time=60 --max-requests=0 run
Therefore reset tree->last on ordered extent removal only if
it pointed to the ordered extent we're removing from the tree.
Results from 4 runs of the following test before and after
applying this patch:
$ sysbench --test=fileio --file-num=32 --file-total-size=4G \
--file-test-mode=seqwr --num-threads=512 \
--file-block-size=32768 --max-time=60 --file-io-mode=sync prepare
$ sysbench --test=fileio --file-num=32 --file-total-size=4G \
--file-test-mode=seqwr --num-threads=512 \
--file-block-size=32768 --max-time=60 --file-io-mode=sync run
Before this path:
run 1 - 64.049Mb/sec
run 2 - 63.455Mb/sec
run 3 - 64.656Mb/sec
run 4 - 63.833Mb/sec
After this patch:
run 1 - 66.149Mb/sec
run 2 - 68.459Mb/sec
run 3 - 66.338Mb/sec
run 4 - 66.176Mb/sec
With random writes (--file-test-mode=rndwr) I had huge fluctuations
on the results (+- 35% easily).
Signed-off-by: Filipe David Borba Manana <fdmanana@gmail.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>
diff --git a/fs/btrfs/ordered-data.c b/fs/btrfs/ordered-data.c
index 69582d5..b8c2ded 100644
--- a/fs/btrfs/ordered-data.c
+++ b/fs/btrfs/ordered-data.c
@@ -520,7 +520,8 @@
spin_lock_irq(&tree->lock);
node = &entry->rb_node;
rb_erase(node, &tree->tree);
- tree->last = NULL;
+ if (tree->last == node)
+ tree->last = NULL;
set_bit(BTRFS_ORDERED_COMPLETE, &entry->flags);
spin_unlock_irq(&tree->lock);
