Btrfs: reduce lock contention during extent insertion
We're spending huge amounts of time on lock contention during
end_io processing because we unconditionally assume we are overwriting
an existing extent in the file for each IO.
This checks to see if we are outside i_size, and if so, it uses a
less expensive readonly search of the btree to look for existing
extents.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index d83260d..53bf2d7 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -567,6 +567,7 @@
int extent_type;
int recow;
int ret;
+ int modify_tree = -1;
if (drop_cache)
btrfs_drop_extent_cache(inode, start, end - 1, 0);
@@ -575,10 +576,13 @@
if (!path)
return -ENOMEM;
+ if (start >= BTRFS_I(inode)->disk_i_size)
+ modify_tree = 0;
+
while (1) {
recow = 0;
ret = btrfs_lookup_file_extent(trans, root, path, ino,
- search_start, -1);
+ search_start, modify_tree);
if (ret < 0)
break;
if (ret > 0 && path->slots[0] > 0 && search_start == start) {
@@ -634,7 +638,8 @@
}
search_start = max(key.offset, start);
- if (recow) {
+ if (recow || !modify_tree) {
+ modify_tree = -1;
btrfs_release_path(path);
continue;
}