Btrfs: Try harder while searching for free space

The loop searching for free space would exit out too soon when
metadata clustering was trying to allocate a large extent.  This makes
sure a full scan of the free space is done searching for only the
minimum extent size requested by the higher layers.

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

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 2451717d36deef1399c33f68dfbeb0c0c14eb378..55d6a66c622d1ef7676ef02681d6131b976782be 100644 (file)
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -2123,6 +2123,7 @@ static int noinline find_free_extent(struct btrfs_trans_handle *trans,
        int allowed_chunk_alloc = 0;
        struct list_head *head = NULL, *cur = NULL;
        int loop = 0;
+       int extra_loop = 0;
        struct btrfs_space_info *space_info;
 
        WARN_ON(num_bytes < root->sectorsize);
@@ -2191,6 +2192,9 @@ static int noinline find_free_extent(struct btrfs_trans_handle *trans,
 
                free_space = btrfs_find_free_space(block_group, search_start,
                                                   total_needed);
+               if (empty_size)
+                       extra_loop = 1;
+
                if (free_space) {
                        u64 start = block_group->key.objectid;
                        u64 end = block_group->key.objectid +
@@ -2254,11 +2258,11 @@ static int noinline find_free_extent(struct btrfs_trans_handle *trans,
 new_group:
                mutex_unlock(&block_group->alloc_mutex);
 new_group_no_lock:
+               /* don't try to compare new allocations against the
+                * last allocation any more
+                */
                last_wanted = 0;
-               if (!allowed_chunk_alloc) {
-                       total_needed -= empty_size;
-                       empty_size = 0;
-               }
+
                /*
                 * Here's how this works.
                 * loop == 0: we were searching a block group via a hint
@@ -2276,9 +2280,21 @@ new_group_no_lock:
                        cur = head->next;
                        loop++;
                } else if (loop == 1 && cur == head) {
-
+                       int keep_going;
+
+                       /* at this point we give up on the empty_size
+                        * allocations and just try to allocate the min
+                        * space.
+                        *
+                        * The extra_loop field was set if an empty_size
+                        * allocation was attempted above, and if this
+                        * is try we need to try the loop again without
+                        * the additional empty_size.
+                        */
                        total_needed -= empty_size;
                        empty_size = 0;
+                       keep_going = extra_loop;
+                       loop++;
 
                        if (allowed_chunk_alloc && !chunk_alloc_done) {
                                up_read(&space_info->groups_sem);
@@ -2287,13 +2303,19 @@ new_group_no_lock:
                                if (ret < 0)
                                        break;
                                down_read(&space_info->groups_sem);
-                               loop++;
                                head = &space_info->block_groups;
-                               cur = head->next;
+                               /*
+                                * we've allocated a new chunk, keep
+                                * trying
+                                */
+                               keep_going = 1;
                                chunk_alloc_done = 1;
                        } else if (!allowed_chunk_alloc) {
                                space_info->force_alloc = 1;
-                               break;
+                       }
+                       if (keep_going) {
+                               cur = head->next;
+                               extra_loop = 0;
                        } else {
                                break;
                        }