Improve sorted scan memory accounting

Since we use two B-trees q_exts_by_size and q_exts_by_addr, we should count 2x sizeof (range_seg_gap_t) per node. And since average B-tree memory efficiency is about 75%, we should increase it to 3x. Previous code under-counted up to 30% of the memory usage. Reviewed-by: Brian Behlendorf <[email protected]> Signed-off-by: Alexander Motin <[email protected]> Sponsored-By: iXsystems, Inc. Closes #13537
openzfs · Jun 10, 2022 · 87b46d6 · 87b46d6
1 parent 4ed5e25
commit 87b46d6
Showing 1 changed file with 5 additions and 2 deletions.
diff --git a/module/zfs/dsl_scan.c b/module/zfs/dsl_scan.c
@@ -1276,9 +1276,12 @@ dsl_scan_should_clear(dsl_scan_t *scn)
 		mutex_enter(&tvd->vdev_scan_io_queue_lock);
 		queue = tvd->vdev_scan_io_queue;
 		if (queue != NULL) {
-			/* # extents in exts_by_size = # in exts_by_addr */
+			/*
+			 * # of extents in exts_by_size = # in exts_by_addr.
+			 * B-tree efficiency is ~75%, but can be as low as 50%.
+			 */
 			mused += zfs_btree_numnodes(&queue->q_exts_by_size) *
-			    sizeof (range_seg_gap_t) + queue->q_sio_memused;
+			    3 * sizeof (range_seg_gap_t) + queue->q_sio_memused;
 		}
 		mutex_exit(&tvd->vdev_scan_io_queue_lock);
 	}