MFV r272803:

Illumos issue:
    5175 implement dmu_read_uio_dbuf() to improve cached read performance

MFC after:	2 weeks

sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu.c

@@ -1021,8 +1021,8 @@ xuio_stat_wbuf_nocopy()
 }
 
 #ifdef _KERNEL
-int
-dmu_read_uio(objset_t *os, uint64_t object, uio_t *uio, uint64_t size)
+static int
+dmu_read_uio_dnode(dnode_t *dn, uio_t *uio, uint64_t size)
 {
 	dmu_buf_t **dbp;
 	int numbufs, i, err;
@@ -1032,8 +1032,8 @@ dmu_read_uio(objset_t *os, uint64_t object, uio_t *uio, uint64_t size)
 	 * NB: we could do this block-at-a-time, but it's nice
 	 * to be reading in parallel.
 	 */
-	err = dmu_buf_hold_array(os, object, uio->uio_loffset, size, TRUE, FTAG,
-	    &numbufs, &dbp);
+	err = dmu_buf_hold_array_by_dnode(dn, uio->uio_loffset, size,
+	    TRUE, FTAG, &numbufs, &dbp, 0);
 	if (err)
 		return (err);
 
@@ -1080,6 +1080,58 @@ dmu_read_uio(objset_t *os, uint64_t object, uio_t *uio, uint64_t size)
 	return (err);
 }
 
+/*
+ * Read 'size' bytes into the uio buffer.
+ * From object zdb->db_object.
+ * Starting at offset uio->uio_loffset.
+ *
+ * If the caller already has a dbuf in the target object
+ * (e.g. its bonus buffer), this routine is faster than dmu_read_uio(),
+ * because we don't have to find the dnode_t for the object.
+ */
+int
+dmu_read_uio_dbuf(dmu_buf_t *zdb, uio_t *uio, uint64_t size)
+{
+	dmu_buf_impl_t *db = (dmu_buf_impl_t *)zdb;
+	dnode_t *dn;
+	int err;
+
+	if (size == 0)
+		return (0);
+
+	DB_DNODE_ENTER(db);
+	dn = DB_DNODE(db);
+	err = dmu_read_uio_dnode(dn, uio, size);
+	DB_DNODE_EXIT(db);
+
+	return (err);
+}
+
+/*
+ * Read 'size' bytes into the uio buffer.
+ * From the specified object
+ * Starting at offset uio->uio_loffset.
+ */
+int
+dmu_read_uio(objset_t *os, uint64_t object, uio_t *uio, uint64_t size)
+{
+	dnode_t *dn;
+	int err;
+
+	if (size == 0)
+		return (0);
+
+	err = dnode_hold(os, object, FTAG, &dn);
+	if (err)
+		return (err);
+
+	err = dmu_read_uio_dnode(dn, uio, size);
+
+	dnode_rele(dn, FTAG);
+
+	return (err);
+}
+
 static int
 dmu_write_uio_dnode(dnode_t *dn, uio_t *uio, uint64_t size, dmu_tx_t *tx)
 {
@@ -1132,6 +1184,15 @@ dmu_write_uio_dnode(dnode_t *dn, uio_t *uio, uint64_t size, dmu_tx_t *tx)
 	return (err);
 }
 
+/*
+ * Write 'size' bytes from the uio buffer.
+ * To object zdb->db_object.
+ * Starting at offset uio->uio_loffset.
+ *
+ * If the caller already has a dbuf in the target object
+ * (e.g. its bonus buffer), this routine is faster than dmu_write_uio(),
+ * because we don't have to find the dnode_t for the object.
+ */
 int
 dmu_write_uio_dbuf(dmu_buf_t *zdb, uio_t *uio, uint64_t size,
     dmu_tx_t *tx)
@@ -1151,6 +1212,11 @@ dmu_write_uio_dbuf(dmu_buf_t *zdb, uio_t *uio, uint64_t size,
 	return (err);
 }
 
+/*
+ * Write 'size' bytes from the uio buffer.
+ * To the specified object.
+ * Starting at offset uio->uio_loffset.
+ */
 int
 dmu_write_uio(objset_t *os, uint64_t object, uio_t *uio, uint64_t size,
     dmu_tx_t *tx)

sys/cddl/contrib/opensolaris/uts/common/fs/zfs/sys/dmu.h

@@ -616,6 +616,7 @@ void dmu_write(objset_t *os, uint64_t object, uint64_t offset, uint64_t size,
 void dmu_prealloc(objset_t *os, uint64_t object, uint64_t offset, uint64_t size,
 	dmu_tx_t *tx);
 int dmu_read_uio(objset_t *os, uint64_t object, struct uio *uio, uint64_t size);
+int dmu_read_uio_dbuf(dmu_buf_t *zdb, struct uio *uio, uint64_t size);
 int dmu_write_uio(objset_t *os, uint64_t object, struct uio *uio, uint64_t size,
     dmu_tx_t *tx);
 int dmu_write_uio_dbuf(dmu_buf_t *zdb, struct uio *uio, uint64_t size,

sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vnops.c

@@ -582,7 +582,6 @@ static int
 mappedread(vnode_t *vp, int nbytes, uio_t *uio)
 {
 	znode_t *zp = VTOZ(vp);
-	objset_t *os = zp->z_zfsvfs->z_os;
 	vm_object_t obj;
 	int64_t start;
 	caddr_t va;
@@ -613,7 +612,8 @@ mappedread(vnode_t *vp, int nbytes, uio_t *uio)
 			page_unhold(pp);
 		} else {
 			zfs_vmobject_wunlock(obj);
-			error = dmu_read_uio(os, zp->z_id, uio, bytes);
+			error = dmu_read_uio_dbuf(sa_get_db(zp->z_sa_hdl),
+			    uio, bytes);
 			zfs_vmobject_wlock(obj);
 		}
 		len -= bytes;
@@ -650,7 +650,6 @@ zfs_read(vnode_t *vp, uio_t *uio, int ioflag, cred_t *cr, caller_context_t *ct)
 {
 	znode_t		*zp = VTOZ(vp);
 	zfsvfs_t	*zfsvfs = zp->z_zfsvfs;
-	objset_t	*os;
 	ssize_t		n, nbytes;
 	int		error = 0;
 	rl_t		*rl;
@@ -658,7 +657,6 @@ zfs_read(vnode_t *vp, uio_t *uio, int ioflag, cred_t *cr, caller_context_t *ct)
 
 	ZFS_ENTER(zfsvfs);
 	ZFS_VERIFY_ZP(zp);
-	os = zfsvfs->z_os;
 
 	if (zp->z_pflags & ZFS_AV_QUARANTINED) {
 		ZFS_EXIT(zfsvfs);
@@ -756,10 +754,12 @@ zfs_read(vnode_t *vp, uio_t *uio, int ioflag, cred_t *cr, caller_context_t *ct)
 			error = mappedread_sf(vp, nbytes, uio);
 		else
 #endif /* __FreeBSD__ */
-		if (vn_has_cached_data(vp))
+		if (vn_has_cached_data(vp)) {
 			error = mappedread(vp, nbytes, uio);
-		else
-			error = dmu_read_uio(os, zp->z_id, uio, nbytes);
+		} else {
+			error = dmu_read_uio_dbuf(sa_get_db(zp->z_sa_hdl),
+			    uio, nbytes);
+		}
 		if (error) {
 			/* convert checksum errors into IO errors */
 			if (error == ECKSUM)