Btrfs: enforce metadata allocation clustering

The allocator uses the last allocation as a starting point for metadata
allocations, and tries to allocate in clusters of at least 256k.

If the search for a free block fails to find the expected block, this patch
forces a new cluster to be found in the free list.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 17 insertions, 0 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index ebd8275a193..b8c6541c33f 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -2195,6 +2195,23 @@ static int noinline find_free_extent(struct btrfs_trans_handle *trans,
                         if (search_start + num_bytes > end)
                                 goto new_group;
 
+                        if (last_ptr && *last_ptr && search_start != *last_ptr) {
+                                total_needed += empty_cluster;
+                                *last_ptr = 0;
+                                /*
+                                 * if search_start is still in this block group
+                                 * then we just re-search this block group
+                                 */
+                                if (search_start >= start &&
+                                    search_start < end) {
+                                        mutex_unlock(&block_group->alloc_mutex);
+                                        continue;
+                                }
+
+                                /* else we go to the next block group */
+                                goto new_group;
+                        }
+
                         if (exclude_nr > 0 &&
                             (search_start + num_bytes > exclude_start &&
                              search_start < exclude_start + exclude_nr)) {