ZIO: Optimize zio_flush()

- Generalize vdev_nowritecache handling by traversing through the VDEV tree and skipping children ZIOs where not supported. - Remove intermediate zio_null() in case of several VDEV children. - Remove children handling from zio_ioctl(). There are no other use cases for this code beside DKIOCFLUSHWRITECACHED, and would there be, I doubt they would so straightforward apply to all VDEV children. Comparing to removed previous optimization this should improve cases of redundant ZILs/SLOGs. Reviewed-by: Brian Behlendorf <[email protected]> Reviewed-by: George Wilson <[email protected]> Signed-off-by: Alexander Motin <[email protected]> Sponsored by: iXsystems, Inc. Closes #15515
openzfs · Apr 19, 2024 · 8b1a132 · 8b1a132
1 parent 7ea8331
commit 8b1a132
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Showing 2 changed files with 16 additions and 22 deletions.
diff --git a/module/zfs/zil.c b/module/zfs/zil.c
@@ -1622,7 +1622,7 @@ zil_lwb_write_done(zio_t *zio)
 
 	while ((zv = avl_destroy_nodes(t, &cookie)) != NULL) {
 		vdev_t *vd = vdev_lookup_top(spa, zv->zv_vdev);
-		if (vd != NULL && !vd->vdev_nowritecache) {
+		if (vd != NULL) {
 			/*
 			 * The "ZIO_FLAG_DONT_PROPAGATE" is currently
 			 * always used within "zio_flush". This means,

diff --git a/module/zfs/zio.c b/module/zfs/zio.c
@@ -1435,23 +1435,10 @@ zio_t *
 zio_ioctl(zio_t *pio, spa_t *spa, vdev_t *vd, int cmd,
     zio_done_func_t *done, void *private, zio_flag_t flags)
 {
-	zio_t *zio;
-	int c;
-
-	if (vd->vdev_children == 0) {
-		zio = zio_create(pio, spa, 0, NULL, NULL, 0, 0, done, private,
-		    ZIO_TYPE_IOCTL, ZIO_PRIORITY_NOW, flags, vd, 0, NULL,
-		    ZIO_STAGE_OPEN, ZIO_IOCTL_PIPELINE);
-
-		zio->io_cmd = cmd;
-	} else {
-		zio = zio_null(pio, spa, NULL, NULL, NULL, flags);
-
-		for (c = 0; c < vd->vdev_children; c++)
-			zio_nowait(zio_ioctl(zio, spa, vd->vdev_child[c], cmd,
-			    done, private, flags));
-	}
-
+	zio_t *zio = zio_create(pio, spa, 0, NULL, NULL, 0, 0, done, private,
+	    ZIO_TYPE_IOCTL, ZIO_PRIORITY_NOW, flags, vd, 0, NULL,
+	    ZIO_STAGE_OPEN, ZIO_IOCTL_PIPELINE);
+	zio->io_cmd = cmd;
 	return (zio);
 }
 
@@ -1622,11 +1609,18 @@ zio_vdev_delegated_io(vdev_t *vd, uint64_t offset, abd_t *data, uint64_t size,
 }
 
 void
-zio_flush(zio_t *zio, vdev_t *vd)
+zio_flush(zio_t *pio, vdev_t *vd)
 {
-	zio_nowait(zio_ioctl(zio, zio->io_spa, vd, DKIOCFLUSHWRITECACHE,
-	    NULL, NULL,
-	    ZIO_FLAG_CANFAIL | ZIO_FLAG_DONT_PROPAGATE | ZIO_FLAG_DONT_RETRY));
+	if (vd->vdev_nowritecache)
+		return;
+	if (vd->vdev_children == 0) {
+		zio_nowait(zio_ioctl(pio, vd->vdev_spa, vd,
+		    DKIOCFLUSHWRITECACHE, NULL, NULL, ZIO_FLAG_CANFAIL |
+		    ZIO_FLAG_DONT_PROPAGATE | ZIO_FLAG_DONT_RETRY));
+	} else {
+		for (uint64_t c = 0; c < vd->vdev_children; c++)
+			zio_flush(pio, vd->vdev_child[c]);
+	}
 }
 
 void