Btrfs: don't continue setting up space cache when enospc

If we hit ENOSPC when setting up a space cache don't bother setting up any of
the other space cache's in this transaction, it'll just induce unnecessary
latency.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>

2 files changed, 20 insertions, 0 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index febb5bc35a64..3185c457f025 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3403,6 +3403,15 @@ again:
         spin_unlock(&block_group->lock);
 
         /*
+         * We hit an ENOSPC when setting up the cache in this transaction, just
+         * skip doing the setup, we've already cleared the cache so we're safe.
+         */
+        if (test_bit(BTRFS_TRANS_CACHE_ENOSPC, &trans->transaction->flags)) {
+                ret = -ENOSPC;
+                goto out_put;
+        }
+
+        /*
          * Try to preallocate enough space based on how big the block group is.
          * Keep in mind this has to include any pinned space which could end up
          * taking up quite a bit since it's not folded into the other space
@@ -3422,8 +3431,18 @@ again:
         ret = btrfs_prealloc_file_range_trans(inode, trans, 0, 0, num_pages,
                                               num_pages, num_pages,
                                               &alloc_hint);
+        /*
+         * Our cache requires contiguous chunks so that we don't modify a bunch
+         * of metadata or split extents when writing the cache out, which means
+         * we can enospc if we are heavily fragmented in addition to just normal
+         * out of space conditions.  So if we hit this just skip setting up any
+         * other block groups for this transaction, maybe we'll unpin enough
+         * space the next time around.
+         */
         if (!ret)
                 dcs = BTRFS_DC_SETUP;
+        else if (ret == -ENOSPC)
+                set_bit(BTRFS_TRANS_CACHE_ENOSPC, &trans->transaction->flags);
         btrfs_free_reserved_data_space(inode, num_pages);
 
 out_put:
diff --git a/fs/btrfs/transaction.h b/fs/btrfs/transaction.h
index 109b8b7fb48e..30ae75074ca4 100644
--- a/fs/btrfs/transaction.h
+++ b/fs/btrfs/transaction.h
@@ -34,6 +34,7 @@ enum btrfs_trans_state {
 
 #define BTRFS_TRANS_HAVE_FREE_BGS       0
 #define BTRFS_TRANS_DIRTY_BG_RUN        1
+#define BTRFS_TRANS_CACHE_ENOSPC        2
 
 struct btrfs_transaction {
         u64 transid;