Btrfs: wait on async pages when shrinking delalloc

Mitch reported a problem where you could get an ENOSPC error when untarring
a kernel git tree onto a 16gb file system with compress-force=zlib.  This is
because compression is a huge pain, it will return from ->writepages()
without having actually created any ordered extents.  To get around this we
check to see if the async submit counter is up, and if it is wait until it
drops to 0 before doing our normal ordered wait dance.  With this patch I
can now untar a kernel git tree onto a 16gb file system without getting
ENOSPC errors.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index b6b33e463ac3e4ea240dcbb59c351fe89a4bc90c..06369d588f2734437bb7a187814798004e1b8029 100644 (file)
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3697,6 +3697,13 @@ static void shrink_delalloc(struct btrfs_root *root, u64 to_reclaim, u64 orig,
                writeback_inodes_sb_nr_if_idle(root->fs_info->sb, nr_pages,
                                               WB_REASON_FS_FREE_SPACE);
 
+               /*
+                * We need to wait for the async pages to actually start before
+                * we do anything.
+                */
+               wait_event(root->fs_info->async_submit_wait,
+                          !atomic_read(&root->fs_info->async_delalloc_pages));
+
                spin_lock(&space_info->lock);
                if (space_info->bytes_used + space_info->bytes_reserved +
                    space_info->bytes_pinned + space_info->bytes_readonly +