Btrfs: avoid allocation clusters that are too spread out

In SSD mode for data, and all the time for metadata the allocator
will try to find a cluster of nearby blocks for allocations.  This
commit adds extra checks to make sure that each free block in the
cluster is close to the last one.

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

diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
index 2801655..ac23476 100644 (file)
--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -645,7 +645,8 @@ again:
                 * we haven't filled the empty size and the window is
                 * very large.  reset and try again
                 */
-               if (next->offset - window_start > (bytes + empty_size) * 2) {
+               if (next->offset - (last->offset + last->bytes) > 128 * 1024 ||
+                   next->offset - window_start > (bytes + empty_size) * 2) {
                        entry = next;
                        window_start = entry->offset;
                        window_free = entry->bytes;