xfs: add a tracepoint for blockgc scans

Add some tracepoints so that we can observe when the speculative
preallocation garbage collector runs.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index 38ee66d..3ddefb6 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -2339,6 +2339,8 @@ xfs_file_ioctl(
 		if (error)
 			return error;
 
+		trace_xfs_ioc_free_eofblocks(mp, &keofb, _RET_IP_);
+
 		sb_start_write(mp->m_super);
 		error = xfs_icache_free_eofblocks(mp, &keofb);
 		sb_end_write(mp->m_super);