Btrfs: Tune readahead during defrag to avoid reading too much at once

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

1 files changed, 28 insertions, 13 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 1cf125ab7822..c4fe37791d3f 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -1856,27 +1856,44 @@ static int noinline drop_leaf_ref(struct btrfs_trans_handle *trans,
 }
 
 static void noinline reada_walk_down(struct btrfs_root *root,
-                                     struct extent_buffer *node)
+                                     struct extent_buffer *node,
+                                     int slot)
 {
-        int i;
-        u32 nritems;
         u64 bytenr;
-        int ret;
+        u64 last = 0;
+        u32 nritems;
         u32 refs;
-        int level;
         u32 blocksize;
+        int ret;
+        int i;
+        int level;
+        int skipped = 0;
 
         nritems = btrfs_header_nritems(node);
         level = btrfs_header_level(node);
-        for (i = 0; i < nritems; i++) {
+        if (level)
+                return;
+
+        for (i = slot; i < nritems && skipped < 32; i++) {
                 bytenr = btrfs_node_blockptr(node, i);
-                blocksize = btrfs_level_size(root, level - 1);
-                ret = lookup_extent_ref(NULL, root, bytenr, blocksize, &refs);
-                BUG_ON(ret);
-                if (refs != 1)
+                if (last && ((bytenr > last && bytenr - last > 32 * 1024) ||
+                             (last > bytenr && last - bytenr > 32 * 1024))) {
+                        skipped++;
                         continue;
+                }
+                blocksize = btrfs_level_size(root, level - 1);
+                if (i != slot) {
+                        ret = lookup_extent_ref(NULL, root, bytenr,
+                                                blocksize, &refs);
+                        BUG_ON(ret);
+                        if (refs != 1) {
+                                skipped++;
+                                continue;
+                        }
+                }
                 mutex_unlock(&root->fs_info->fs_mutex);
                 ret = readahead_tree_block(root, bytenr, blocksize);
+                last = bytenr + blocksize;
                 cond_resched();
                 mutex_lock(&root->fs_info->fs_mutex);
                 if (ret)
@@ -1919,9 +1936,6 @@ static int noinline walk_down_tree(struct btrfs_trans_handle *trans,
                 WARN_ON(*level >= BTRFS_MAX_LEVEL);
                 cur = path->nodes[*level];
 
-                if (*level > 0 && path->slots[*level] == 0)
-                        reada_walk_down(root, cur);
-
                 if (btrfs_header_level(cur) != *level)
                         WARN_ON(1);
 
@@ -1951,6 +1965,7 @@ static int noinline walk_down_tree(struct btrfs_trans_handle *trans,
                 next = btrfs_find_tree_block(root, bytenr, blocksize);
                 if (!next || !btrfs_buffer_uptodate(next)) {
                         free_extent_buffer(next);
+                        reada_walk_down(root, cur, path->slots[*level]);
                         mutex_unlock(&root->fs_info->fs_mutex);
                         next = read_tree_block(root, bytenr, blocksize);
                         mutex_lock(&root->fs_info->fs_mutex);