btrfs: add more find_free_extent tracepoints

find_free_extent is a complicated function. It consists (at least) of:

- a hint that jumps into the middle of a for loop macro
- a middle loop trying every raid level
- an outer loop ascending through ffe loop levels
- complicated logic for skipping some of those ffe loop levels
- multiple underlying in-bg allocators (zoned, cluster, no cluster)

Which is all to say that more tracing is helpful for debugging its
behavior. Add two new tracepoints: at the entrance to the block_groups
loop (hit for every raid level and every ffe_ctl loop) and at the point
we seriously consider a block_group for allocation. This way we can see
the whole path through the algorithm, including hints, multiple loops,
etc.

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Boris Burkov <boris@bur.io>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index b26cbf6cae8b..203c8cbb9983 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -4261,6 +4261,7 @@ static noinline int find_free_extent(struct btrfs_root *root,
 							block_group->flags);
 				btrfs_lock_block_group(block_group,
 						       ffe_ctl->delalloc);
+				ffe_ctl->hinted = true;
 				goto have_block_group;
 			}
 		} else if (block_group) {
@@ -4268,6 +4269,7 @@ static noinline int find_free_extent(struct btrfs_root *root,
 		}
 	}
 search:
+	trace_find_free_extent_search_loop(root, ffe_ctl);
 	ffe_ctl->have_caching_bg = false;
 	if (ffe_ctl->index == btrfs_bg_flags_to_raid_index(ffe_ctl->flags) ||
 	    ffe_ctl->index == 0)
@@ -4277,6 +4279,7 @@ search:
 			    &space_info->block_groups[ffe_ctl->index], list) {
 		struct btrfs_block_group *bg_ret;
 
+		ffe_ctl->hinted = false;
 		/* If the block group is read-only, we can skip it entirely. */
 		if (unlikely(block_group->ro)) {
 			if (ffe_ctl->for_treelog)
@@ -4318,6 +4321,7 @@ search:
 		}
 
 have_block_group:
+		trace_find_free_extent_have_block_group(root, ffe_ctl, block_group);
 		ffe_ctl->cached = btrfs_block_group_done(block_group);
 		if (unlikely(!ffe_ctl->cached)) {
 			ffe_ctl->have_caching_bg = true;