Fix zfs_vdev_aggregation_limit bounds checking

Update the bounds checking for zfs_vdev_aggregation_limit so that
it has a floor of zero and a maximum value of the supported block
size for the pool.

Additionally add an early return when zfs_vdev_aggregation_limit
equals zero to disable aggregation.  For very fast solid state or
memory devices it may be more expensive to perform the aggregation
than to issue the IO immediately.

Signed-off-by: Brian Behlendorf <[email protected]>

1 files changed, 8 insertions, 11 deletions

diff --git a/module/zfs/vdev_queue.c b/module/zfs/vdev_queue.c
index 0c62a6fa3..e828ce917 100644
--- a/module/zfs/vdev_queue.c
+++ b/module/zfs/vdev_queue.c
@@ -499,20 +499,17 @@ vdev_queue_aggregate(vdev_queue_t *vq, zio_t *zio)
 	zio_t *first, *last, *aio, *dio, *mandatory, *nio;
 	uint64_t maxgap = 0;
 	uint64_t size;
+	uint64_t limit;
 	boolean_t stretch = B_FALSE;
 	avl_tree_t *t = vdev_queue_type_tree(vq, zio->io_type);
 	enum zio_flag flags = zio->io_flags & ZIO_FLAG_AGG_INHERIT;
 	void *buf;
 
-	if (zio->io_flags & ZIO_FLAG_DONT_AGGREGATE)
-		return (NULL);
+	limit = MAX(MIN(zfs_vdev_aggregation_limit,
+	    spa_maxblocksize(vq->vq_vdev->vdev_spa)), 0);
 
-	/*
-	 * Prevent users from setting the zfs_vdev_aggregation_limit
-	 * tuning larger than SPA_MAXBLOCKSIZE.
-	 */
-	zfs_vdev_aggregation_limit =
-	    MIN(zfs_vdev_aggregation_limit, SPA_MAXBLOCKSIZE);
+	if (zio->io_flags & ZIO_FLAG_DONT_AGGREGATE || limit == 0)
+		return (NULL);
 
 	first = last = zio;
 
@@ -540,7 +537,7 @@ vdev_queue_aggregate(vdev_queue_t *vq, zio_t *zio)
 	 */
 	while ((dio = AVL_PREV(t, first)) != NULL &&
 	    (dio->io_flags & ZIO_FLAG_AGG_INHERIT) == flags &&
-	    IO_SPAN(dio, last) <= zfs_vdev_aggregation_limit &&
+	    IO_SPAN(dio, last) <= limit &&
 	    IO_GAP(dio, first) <= maxgap) {
 		first = dio;
 		if (mandatory == NULL && !(first->io_flags & ZIO_FLAG_OPTIONAL))
@@ -561,7 +558,7 @@ vdev_queue_aggregate(vdev_queue_t *vq, zio_t *zio)
 	 */
 	while ((dio = AVL_NEXT(t, last)) != NULL &&
 	    (dio->io_flags & ZIO_FLAG_AGG_INHERIT) == flags &&
-	    IO_SPAN(first, dio) <= zfs_vdev_aggregation_limit &&
+	    IO_SPAN(first, dio) <= limit &&
 	    IO_GAP(last, dio) <= maxgap) {
 		last = dio;
 		if (!(last->io_flags & ZIO_FLAG_OPTIONAL))
@@ -607,7 +604,7 @@ vdev_queue_aggregate(vdev_queue_t *vq, zio_t *zio)
 		return (NULL);
 
 	size = IO_SPAN(first, last);
-	ASSERT3U(size, <=, zfs_vdev_aggregation_limit);
+	ASSERT3U(size, <=, limit);
 
 	buf = zio_buf_alloc_flags(size, KM_NOSLEEP);
 	if (buf == NULL)