Btrfs: Limit btree writeback to prevent seeks

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

1 files changed, 9 insertions, 0 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 3e16cca72b49..28e9ef8a3253 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -210,6 +210,15 @@ static int btree_writepages(struct address_space *mapping,
 {
         struct extent_map_tree *tree;
         tree = &BTRFS_I(mapping->host)->extent_tree;
+        if (wbc->sync_mode == WB_SYNC_NONE) {
+                u64 num_dirty;
+                u64 start = 0;
+                unsigned long thresh = 96 * 1024 * 1024;
+                num_dirty = count_range_bits(tree, &start, thresh, EXTENT_DIRTY);
+                if (num_dirty < thresh) {
+                        return 0;
+                }
+        }
         return extent_writepages(tree, mapping, btree_get_extent, wbc);
 }