Allocate ABD buffer according to BUFC type in _cb functions

In dsl_scan_scrub_cb and spa_load_verify_cb, we originally always allocated
linear ABD. Now we try to allocate scatter ABD according to the BUFC type of
the blkptr to reduce unnecessary spl slab allocation.

Also in zio_ddt_read_start, we match the parent zio->io_data ABD type for the
same reason.

Signed-off-by: Chunwei Chen <tuxoko@gmail.com>

module/zfs/dsl_scan.c

@@ -1830,7 +1830,12 @@ dsl_scan_scrub_cb(dsl_pool_t *dp,
 	if (needs_io && !zfs_no_scrub_io) {
 		vdev_t *rvd = spa->spa_root_vdev;
 		uint64_t maxinflight = rvd->vdev_children * zfs_top_maxinflight;
-		abd_t *data = abd_alloc_linear(size);
+		abd_t *data;
+
+		if (ARC_BUFC_IS_SCATTER(BP_GET_BUFC_TYPE(bp)))
+			data = abd_alloc_scatter(size);
+		else
+			data = abd_alloc_linear(size);
 
 		mutex_enter(&spa->spa_scrub_lock);
 		while (spa->spa_scrub_inflight >= maxinflight)

module/zfs/spa.c

@@ -1934,7 +1934,10 @@ spa_load_verify_cb(spa_t *spa, zilog_t *zilog, const blkptr_t *bp,
 
 	rio = arg;
 	size = BP_GET_PSIZE(bp);
-	data = abd_alloc_linear(size);
+	if (ARC_BUFC_IS_SCATTER(BP_GET_BUFC_TYPE(bp)))
+		data = abd_alloc_scatter(size);
+	else
+		data = abd_alloc_linear(size);
 
 	mutex_enter(&spa->spa_scrub_lock);
 	while (spa->spa_scrub_inflight >= spa_load_verify_maxinflight)

module/zfs/zio.c

@@ -2229,13 +2229,17 @@ zio_ddt_read_start(zio_t *zio)
 			return (ZIO_PIPELINE_CONTINUE);
 
 		for (p = 0; p < DDT_PHYS_TYPES; p++, ddp++) {
+			abd_t *tmp;
 			if (ddp->ddp_phys_birth == 0 || ddp == ddp_self)
 				continue;
 			ddt_bp_create(ddt->ddt_checksum, &dde->dde_key, ddp,
 			    &blk);
+			if (ABD_IS_LINEAR(zio->io_data))
+				tmp = abd_alloc_linear(zio->io_size);
+			else
+				tmp = abd_alloc_scatter(zio->io_size);
 			zio_nowait(zio_read(zio, zio->io_spa, &blk,
-			    abd_alloc_linear(zio->io_size),
-			    zio->io_size, zio_ddt_child_read_done, dde,
+			    tmp, zio->io_size, zio_ddt_child_read_done, dde,
 			    zio->io_priority, ZIO_DDT_CHILD_FLAGS(zio) |
 			    ZIO_FLAG_DONT_PROPAGATE, &zio->io_bookmark));
 		}