xfs: iscan batching should handle unallocated inodes too

The inode scanner tries to reduce contention on the AGI header buffer
lock by grabbing references to consecutive allocated inodes.  Batching
stops as soon as we encounter an unallocated inode.  This is unfortunate
because in the worst case performance collapses to the old "one at a
time" behavior if every other inode is free.

This is correct behavior, but we could do better.  Unallocated inodes by
definition have nothing to scan, which means the iscan can ignore them
as long as someone ensures that the scan data will reflect another
thread allocating the inode and adding interesting metadata to that
inode.  That mechanism is, of course, the live update hooks.

Therefore, extend the batching mechanism to track unallocated inodes
adjacent to the scan cursor.  The _want_live_update predicate can tell
the caller's live update hook to incorporate all live updates to what
the scanner thinks is an unallocated inode if (after dropping the AGI)
some other thread allocates one of those inodes and begins using it.

Note that we cannot just copy the ir_free bitmap into the scan cursor
because the batching stops if iget says the inode is in an intermediate
state (e.g. on the inactivation list) and cannot be igrabbed.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

1 files changed, 17 insertions, 4 deletions

diff --git a/fs/xfs/scrub/trace.h b/fs/xfs/scrub/trace.h
index 38d3356466cd..829c90da59c7 100644
--- a/fs/xfs/scrub/trace.h
+++ b/fs/xfs/scrub/trace.h
@@ -1172,6 +1172,7 @@ DEFINE_EVENT(xchk_iscan_class, name, \
 	TP_ARGS(iscan))
 DEFINE_ISCAN_EVENT(xchk_iscan_move_cursor);
 DEFINE_ISCAN_EVENT(xchk_iscan_visit);
+DEFINE_ISCAN_EVENT(xchk_iscan_skip);
 DEFINE_ISCAN_EVENT(xchk_iscan_advance_ag);
 
 DECLARE_EVENT_CLASS(xchk_iscan_ino_class,
@@ -1229,25 +1230,37 @@ TRACE_EVENT(xchk_iscan_iget,
 
 TRACE_EVENT(xchk_iscan_iget_batch,
 	TP_PROTO(struct xfs_mount *mp, struct xchk_iscan *iscan,
-		 unsigned int nr),
-	TP_ARGS(mp, iscan, nr),
+		 unsigned int nr, unsigned int avail),
+	TP_ARGS(mp, iscan, nr, avail),
 	TP_STRUCT__entry(
 		__field(dev_t, dev)
 		__field(xfs_ino_t, cursor)
 		__field(xfs_ino_t, visited)
 		__field(unsigned int, nr)
+		__field(unsigned int, avail)
+		__field(unsigned int, unavail)
+		__field(xfs_ino_t, batch_ino)
+		__field(unsigned long long, skipmask)
 	),
 	TP_fast_assign(
 		__entry->dev = mp->m_super->s_dev;
 		__entry->cursor = iscan->cursor_ino;
 		__entry->visited = iscan->__visited_ino;
 		__entry->nr = nr;
+		__entry->avail = avail;
+		__entry->unavail = hweight64(iscan->__skipped_inomask);
+		__entry->batch_ino = iscan->__batch_ino;
+		__entry->skipmask = iscan->__skipped_inomask;
 	),
-	TP_printk("dev %d:%d iscan cursor 0x%llx visited 0x%llx nr %d",
+	TP_printk("dev %d:%d iscan cursor 0x%llx visited 0x%llx batchino 0x%llx skipmask 0x%llx nr %u avail %u unavail %u",
 		  MAJOR(__entry->dev), MINOR(__entry->dev),
 		  __entry->cursor,
 		  __entry->visited,
-		  __entry->nr)
+		  __entry->batch_ino,
+		  __entry->skipmask,
+		  __entry->nr,
+		  __entry->avail,
+		  __entry->unavail)
 );
 
 TRACE_EVENT(xchk_iscan_iget_retry_wait,