sync: serialise per-superblock sync operations
When competing sync(2) calls walk the same filesystem, they need to
walk the list of inodes on the superblock to find all the inodes
that we need to wait for IO completion on. However, when multiple
wait_sb_inodes() calls do this at the same time, they contend on the
the inode_sb_list_lock and the contention causes system wide
slowdowns. In effect, concurrent sync(2) calls can take longer and
burn more CPU than if they were serialised.
Stop the worst of the contention by adding a per-sb mutex to wrap
around wait_sb_inodes() so that we only execute one sync(2) IO
completion walk per superblock superblock at a time and hence avoid
contention being triggered by concurrent sync(2) calls.
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: Dave Chinner <dchinner@redhat.com>
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 09bbd38..82dfc55 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1375,6 +1375,8 @@
struct list_lru s_inode_lru ____cacheline_aligned_in_smp;
struct rcu_head rcu;
+ struct mutex s_sync_lock; /* sync serialisation lock */
+
/*
* Indicates how deep in a filesystem stack this SB is
*/