dnode: allow storage class to be overridden by object type

spa_preferred_class() selects a storage class based on (among other
things) the DMU object type. This only works for old-style object types
that match only one specific kind of thing. For DMU_OTN_ types we need
another way to signal the storage class.

This commit allows the object type to be overridden in the IO policy for
the purposes of choosing a storage class. It then adds the ability to
set the storage type on a dnode hold, such that all writes generated
under that hold will get it.

This method has two shortcomings:

- it would be better if we could "name" a set of storage class
  preferences rather than it being implied by the object type.
- it would be better if this info were stored in the dnode on disk.

In the absence of those things, this seems like the smallest possible
change.

Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
Sponsored-by: Klara, Inc.
Sponsored-by: iXsystems, Inc.
Closes #15894

include/sys/dnode.h

@@ -380,6 +380,9 @@ struct dnode {
 
 	/* holds prefetch structure */
 	struct zfetch	dn_zfetch;
+
+	/* Not in dn_phys, but should be. set it after taking a hold */
+	dmu_object_type_t dn_storage_type;	/* type for storage class */
 };
 
 /*
@@ -462,6 +465,8 @@ void dnode_evict_dbufs(dnode_t *dn);
 void dnode_evict_bonus(dnode_t *dn);
 void dnode_free_interior_slots(dnode_t *dn);
 
+void dnode_set_storage_type(dnode_t *dn, dmu_object_type_t type);
+
 #define	DNODE_IS_DIRTY(_dn)						\
 	((_dn)->dn_dirty_txg >= spa_syncing_txg((_dn)->dn_objset->os_spa))
 

include/sys/zio.h

@@ -356,6 +356,7 @@ typedef struct zio_prop {
 	uint8_t			zp_iv[ZIO_DATA_IV_LEN];
 	uint8_t			zp_mac[ZIO_DATA_MAC_LEN];
 	uint32_t		zp_zpl_smallblk;
+	dmu_object_type_t	zp_storage_type;
 } zio_prop_t;
 
 typedef struct zio_cksum_report zio_cksum_report_t;

module/zfs/dmu.c

@@ -2362,6 +2362,7 @@ dmu_write_policy(objset_t *os, dnode_t *dn, int level, int wp, zio_prop_t *zp)
 	memset(zp->zp_mac, 0, ZIO_DATA_MAC_LEN);
 	zp->zp_zpl_smallblk = DMU_OT_IS_FILE(zp->zp_type) ?
 	    os->os_zpl_special_smallblock : 0;
+	zp->zp_storage_type = dn ? dn->dn_storage_type : DMU_OT_NONE;
 
 	ASSERT3U(zp->zp_compress, !=, ZIO_COMPRESS_INHERIT);
 }

module/zfs/dnode.c

@@ -543,6 +543,17 @@ dnode_setbonus_type(dnode_t *dn, dmu_object_type_t newtype, dmu_tx_t *tx)
 	rw_exit(&dn->dn_struct_rwlock);
 }
 
+void
+dnode_set_storage_type(dnode_t *dn, dmu_object_type_t newtype)
+{
+	/*
+	 * This is not in the dnode_phys, but it should be, and perhaps one day
+	 * will. For now we require it be set after taking a hold.
+	 */
+	ASSERT3U(zfs_refcount_count(&dn->dn_holds), >=, 1);
+	dn->dn_storage_type = newtype;
+}
+
 void
 dnode_rm_spill(dnode_t *dn, dmu_tx_t *tx)
 {
@@ -604,6 +615,8 @@ dnode_create(objset_t *os, dnode_phys_t *dnp, dmu_buf_impl_t *db,
 	dn->dn_have_spill = ((dnp->dn_flags & DNODE_FLAG_SPILL_BLKPTR) != 0);
 	dn->dn_id_flags = 0;
 
+	dn->dn_storage_type = DMU_OT_NONE;
+
 	dmu_zfetch_init(&dn->dn_zfetch, dn);
 
 	ASSERT(DMU_OT_IS_VALID(dn->dn_phys->dn_type));
@@ -687,6 +700,8 @@ dnode_destroy(dnode_t *dn)
 	dn->dn_newprojid = ZFS_DEFAULT_PROJID;
 	dn->dn_id_flags = 0;
 
+	dn->dn_storage_type = DMU_OT_NONE;
+
 	dmu_zfetch_fini(&dn->dn_zfetch);
 	kmem_cache_free(dnode_cache, dn);
 	arc_space_return(sizeof (dnode_t), ARC_SPACE_DNODE);
@@ -946,6 +961,7 @@ dnode_move_impl(dnode_t *odn, dnode_t *ndn)
 	ndn->dn_newgid = odn->dn_newgid;
 	ndn->dn_newprojid = odn->dn_newprojid;
 	ndn->dn_id_flags = odn->dn_id_flags;
+	ndn->dn_storage_type = odn->dn_storage_type;
 	dmu_zfetch_init(&ndn->dn_zfetch, ndn);
 
 	/*
@@ -1004,6 +1020,7 @@ dnode_move_impl(dnode_t *odn, dnode_t *ndn)
 	odn->dn_newgid = 0;
 	odn->dn_newprojid = ZFS_DEFAULT_PROJID;
 	odn->dn_id_flags = 0;
+	odn->dn_storage_type = DMU_OT_NONE;
 
 	/*
 	 * Mark the dnode.

module/zfs/spa_misc.c

@@ -2010,7 +2010,16 @@ metaslab_class_t *
 spa_preferred_class(spa_t *spa, const zio_t *zio)
 {
 	const zio_prop_t *zp = &zio->io_prop;
-	dmu_object_type_t objtype = zp->zp_type;
+
+	/*
+	 * Override object type for the purposes of selecting a storage class.
+	 * Primarily for DMU_OTN_ types where we can't explicitly control their
+	 * storage class; instead, choose a static type most closely matches
+	 * what we want.
+	 */
+	dmu_object_type_t objtype =
+	    zp->zp_storage_type == DMU_OT_NONE ?
+	    zp->zp_type : zp->zp_storage_type;
 
 	/*
 	 * ZIL allocations determine their class in zio_alloc_zil().

module/zfs/zio.c

@@ -3069,7 +3069,7 @@ zio_write_gang_block(zio_t *pio, metaslab_class_t *mc)
 		zp.zp_checksum = gio->io_prop.zp_checksum;
 		zp.zp_compress = ZIO_COMPRESS_OFF;
 		zp.zp_complevel = gio->io_prop.zp_complevel;
-		zp.zp_type = DMU_OT_NONE;
+		zp.zp_type = zp.zp_storage_type = DMU_OT_NONE;
 		zp.zp_level = 0;
 		zp.zp_copies = gio->io_prop.zp_copies;
 		zp.zp_dedup = B_FALSE;