[PATCH 2/3] xfs: convert extent alloc debug fallback to errortag

[Brian Foster <bfoster@redhat.com>]

Extent allocation includes multiple algorithms depending on on-disk
state to maintain performance and efficiency. The likely first
candidate is to simply use the rightmost block in the cntbt if
that's where initial lookup landed.

Since this is a common path for larger allocations on freshly
created filesystems, we include some DEBUG mode logic to randomly
fall out of the this algorithm and exercise fallback behavior. Now
that errortags can be enabled by default, convert this logic to an
errortag and drop the unnecessary DEBUG ifdef.

Signed-off-by: Brian Foster <bfoster@redhat.com>
---
 fs/xfs/libxfs/xfs_alloc.c    | 5 +----
 fs/xfs/libxfs/xfs_errortag.h | 4 +++-
 fs/xfs/xfs_error.c           | 3 +++
 3 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
index 7839efe050bf..129c9f690afc 100644
--- a/fs/xfs/libxfs/xfs_alloc.c
+++ b/fs/xfs/libxfs/xfs_alloc.c
@@ -1615,11 +1615,8 @@ xfs_alloc_ag_vextent_lastblock(
 	int			error;
 	int			i;
 
-#ifdef DEBUG
-	/* Randomly don't execute the first algorithm. */
-	if (get_random_u32_below(2))
+	if (XFS_TEST_ERROR(false, args->mp, XFS_ERRTAG_AG_ALLOC_SKIP))
 		return 0;
-#endif
 
 	/*
 	 * Start from the entry that lookup found, sequence through all larger
diff --git a/fs/xfs/libxfs/xfs_errortag.h b/fs/xfs/libxfs/xfs_errortag.h
index a53c5d40e084..c57d26619817 100644
--- a/fs/xfs/libxfs/xfs_errortag.h
+++ b/fs/xfs/libxfs/xfs_errortag.h
@@ -65,7 +65,8 @@
 #define XFS_ERRTAG_WRITE_DELAY_MS			43
 #define XFS_ERRTAG_EXCHMAPS_FINISH_ONE			44
 #define XFS_ERRTAG_METAFILE_RESV_CRITICAL		45
-#define XFS_ERRTAG_MAX					46
+#define XFS_ERRTAG_AG_ALLOC_SKIP			46
+#define XFS_ERRTAG_MAX					47
 
 /*
  * Random factors for above tags, 1 means always, 2 means 1/2 time, etc.
@@ -115,5 +116,6 @@
 #define XFS_RANDOM_WRITE_DELAY_MS			3000
 #define XFS_RANDOM_EXCHMAPS_FINISH_ONE			1
 #define XFS_RANDOM_METAFILE_RESV_CRITICAL		4
+#define XFS_RANDOM_AG_ALLOC_SKIP			2
 
 #endif /* __XFS_ERRORTAG_H_ */
diff --git a/fs/xfs/xfs_error.c b/fs/xfs/xfs_error.c
index 62ac6debcb5e..f1222e4e8c5f 100644
--- a/fs/xfs/xfs_error.c
+++ b/fs/xfs/xfs_error.c
@@ -64,6 +64,7 @@ static unsigned int xfs_errortag_random_default[] = {
 	XFS_RANDOM_WRITE_DELAY_MS,
 	XFS_RANDOM_EXCHMAPS_FINISH_ONE,
 	XFS_RANDOM_METAFILE_RESV_CRITICAL,
+	XFS_RANDOM_AG_ALLOC_SKIP,
 };
 
 struct xfs_errortag_attr {
@@ -187,6 +188,7 @@ XFS_ERRORTAG_ATTR_RW(wb_delay_ms,	XFS_ERRTAG_WB_DELAY_MS);
 XFS_ERRORTAG_ATTR_RW(write_delay_ms,	XFS_ERRTAG_WRITE_DELAY_MS);
 XFS_ERRORTAG_ATTR_RW(exchmaps_finish_one, XFS_ERRTAG_EXCHMAPS_FINISH_ONE);
 XFS_ERRORTAG_ATTR_RW(metafile_resv_crit, XFS_ERRTAG_METAFILE_RESV_CRITICAL);
+__XFS_ERRORTAG_ATTR_RW(ag_alloc_skip,	XFS_ERRTAG_AG_ALLOC_SKIP,	true);
 
 static struct attribute *xfs_errortag_attrs[] = {
 	XFS_ERRORTAG_ATTR_LIST(noerror),
@@ -234,6 +236,7 @@ static struct attribute *xfs_errortag_attrs[] = {
 	XFS_ERRORTAG_ATTR_LIST(write_delay_ms),
 	XFS_ERRORTAG_ATTR_LIST(exchmaps_finish_one),
 	XFS_ERRORTAG_ATTR_LIST(metafile_resv_crit),
+	XFS_ERRORTAG_ATTR_LIST(ag_alloc_skip),
 	NULL,
 };
 ATTRIBUTE_GROUPS(xfs_errortag);
-- 
2.49.0