[PATCH 4/5] btrfs: probe with GFP_NOWAIT for tree block readahead

extent_buffer readahead should not be able to painfully stall a
search_slot and hog tree locks by getting stuck in direct reclaim.

If the allocation fails, that is fine, we simply fail to do the
readahead in that case.

Signed-off-by: Boris Burkov <[email protected]>
---
 fs/btrfs/extent_io.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 94fa9a6c3978..b40d3c47eb0d 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -4737,7 +4737,8 @@ void btrfs_readahead_tree_block(struct btrfs_fs_info *fs_info,
 		.level = level,
 		.transid = gen
 	};
-	struct btrfs_eb_prealloc pa = { 0 };
+	/* Readahead is best effort so prefer to fail rather than block in reclaim. */
+	struct btrfs_eb_prealloc pa = { .supports_nowait = true };
 	struct extent_buffer *eb;
 	int ret;
 
-- 
2.54.0