Btrfs: Limit btree writeback to prevent seeks

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

3 files changed, 51 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);
 }
 
diff --git a/fs/btrfs/extent_map.c b/fs/btrfs/extent_map.c
index 55f272c335c6..b6a4974ecc23 100644
--- a/fs/btrfs/extent_map.c
+++ b/fs/btrfs/extent_map.c
@@ -1106,6 +1106,45 @@ out:
         return found;
 }
 
+u64 count_range_bits(struct extent_map_tree *tree,
+                     u64 *start, u64 max_bytes, unsigned long bits)
+{
+        struct rb_node *node;
+        struct extent_state *state;
+        u64 cur_start = *start;
+        u64 total_bytes = 0;
+        int found = 0;
+
+        write_lock_irq(&tree->lock);
+        /*
+         * this search will find all the extents that end after
+         * our range starts.
+         */
+        node = tree_search(&tree->state, cur_start);
+        if (!node || IS_ERR(node)) {
+                goto out;
+        }
+
+        while(1) {
+                state = rb_entry(node, struct extent_state, rb_node);
+                if ((state->state & bits)) {
+                        total_bytes += state->end - state->start + 1;
+                        if (total_bytes >= max_bytes)
+                                break;
+                        if (!found) {
+                                *start = state->start;
+                                found = 1;
+                        }
+                }
+                node = rb_next(node);
+                if (!node)
+                        break;
+        }
+out:
+        write_unlock_irq(&tree->lock);
+        return total_bytes;
+}
+
 /*
  * helper function to lock both pages and extents in the tree.
  * pages must be locked first.
diff --git a/fs/btrfs/extent_map.h b/fs/btrfs/extent_map.h
index 24ddc8c93461..13c562f7cb6f 100644
--- a/fs/btrfs/extent_map.h
+++ b/fs/btrfs/extent_map.h
@@ -113,6 +113,9 @@ int extent_read_full_page(struct extent_map_tree *tree, struct page *page,
 int __init extent_map_init(void);
 void __exit extent_map_exit(void);
 
+u64 count_range_bits(struct extent_map_tree *tree,
+                     u64 *start, u64 max_bytes, unsigned long bits);
+
 int test_range_bit(struct extent_map_tree *tree, u64 start, u64 end,
                    int bits, int filled);
 int clear_extent_bits(struct extent_map_tree *tree, u64 start, u64 end,