Btrfs: tune btrfs unplug functions for a small number of devices
When btrfs unplugs, it tries to find the correct device to unplug
via search through the extent_map tree. This avoids unplugging
a device that doesn't need it, but is a waste of time for filesystems
with a small number of devices.
This patch checks the total number of devices before doing the
search.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 8efc123..1bb54d6 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1201,6 +1201,16 @@
return;
inode = mapping->host;
+
+ /*
+ * don't do the expensive searching for a small number of
+ * devices
+ */
+ if (BTRFS_I(inode)->root->fs_info->fs_devices->open_devices <= 2) {
+ __unplug_io_fn(bdi, page);
+ return;
+ }
+
offset = page_offset(page);
em_tree = &BTRFS_I(inode)->extent_tree;