diff --git a/scst/include/scst.h b/scst/include/scst.h
index 9af3ce9a3..76bd650ad 100644
--- a/scst/include/scst.h
+++ b/scst/include/scst.h
@@ -543,12 +543,6 @@ enum scst_exec_context {
 /* Set if tgt_dev is RESERVED by another session */
 #define SCST_TGT_DEV_RESERVED		1
 
-/* Set if the corresponding context should be atomic */
-#define SCST_TGT_DEV_AFTER_INIT_WR_ATOMIC	5
-#define SCST_TGT_DEV_AFTER_EXEC_ATOMIC		6
-
-#define SCST_TGT_DEV_CLUST_POOL			11
-
 /*************************************************************
  ** I/O grouping types. Changing them don't forget to change
  ** the corresponding *_STR values in scst_const.h!
@@ -2333,7 +2327,7 @@ struct scst_device {
 	unsigned short dev_double_ua_possible:1;
 
 	/* If set, dev is read only */
-	unsigned short rd_only:1;
+	unsigned short dev_rd_only:1;
 
 	/* Set, if a strictly serialized cmd is waiting blocked */
 	unsigned short strictly_serialized_cmd_waiting:1;
@@ -2542,6 +2536,22 @@ struct scst_tgt_dev {
 	struct sgv_pool *pool;
 	int max_sg_cnt;
 
+	/*************************************************************
+	 ** Tgt_dev's flags
+	 *************************************************************/
+
+	/* Set if tgt_dev is read only (to save extra dereferences) */
+	unsigned int tgt_dev_rd_only:1;
+
+	/* Set if the corresponding context should be atomic */
+	unsigned int tgt_dev_after_init_wr_atomic:1;
+	unsigned int tgt_dev_after_exec_atimic:1;
+
+	/* Set if tgt_dev uses clustered SGV pool */
+	unsigned int tgt_dev_clust_pool:1;
+
+	/**************************************************************/
+
 	/*
 	 * Tgt_dev's async flags. Modified independently to the neighbour
 	 * fields.
@@ -2629,7 +2639,7 @@ struct scst_acg_dev {
 	uint64_t lun; /* device's LUN in this acg */
 
 	/* If set, the corresponding LU is read only */
-	unsigned int rd_only:1;
+	unsigned int acg_dev_rd_only:1;
 
 	struct scst_acg *acg; /* parent acg */
 
diff --git a/scst/src/dev_handlers/scst_user.c b/scst/src/dev_handlers/scst_user.c
index b8b330954..e3477ec98 100644
--- a/scst/src/dev_handlers/scst_user.c
+++ b/scst/src/dev_handlers/scst_user.c
@@ -2676,7 +2676,7 @@ static int dev_user_attach_tgt(struct scst_tgt_dev *tgt_dev)
 	 * memory for SCST local commands, like REPORT LUNS, where there is no
 	 * corresponding ucmd. Otherwise we will crash in dev_user_alloc_sg().
 	 */
-	if (test_bit(SCST_TGT_DEV_CLUST_POOL, &tgt_dev->tgt_dev_flags))
+	if (tgt_dev->tgt_dev_clust_pool)
 		tgt_dev->dh_priv = dev->pool_clust;
 	else
 		tgt_dev->dh_priv = dev->pool;
@@ -2694,7 +2694,7 @@ static int dev_user_attach_tgt(struct scst_tgt_dev *tgt_dev)
 	ucmd->user_cmd.sess.sess_h = (unsigned long)tgt_dev;
 	ucmd->user_cmd.sess.lun = (uint64_t)tgt_dev->lun;
 	ucmd->user_cmd.sess.threads_num = tgt_dev->sess->tgt->tgtt->threads_num;
-	ucmd->user_cmd.sess.rd_only = tgt_dev->acg_dev->rd_only;
+	ucmd->user_cmd.sess.rd_only = tgt_dev->tgt_dev_rd_only;
 	if (tgtt->get_phys_transport_version != NULL)
 		ucmd->user_cmd.sess.phys_transport_version =
 			tgtt->get_phys_transport_version(tgt);
diff --git a/scst/src/dev_handlers/scst_vdisk.c b/scst/src/dev_handlers/scst_vdisk.c
index 03ee51fa9..88e105b5b 100644
--- a/scst/src/dev_handlers/scst_vdisk.c
+++ b/scst/src/dev_handlers/scst_vdisk.c
@@ -606,7 +606,8 @@ static const char *vdev_get_filename(const struct scst_vdisk_dev *virt_dev)
 }
 
 /* Returns fd, use IS_ERR(fd) to get error status */
-static struct file *vdev_open_fd(const struct scst_vdisk_dev *virt_dev)
+static struct file *vdev_open_fd(const struct scst_vdisk_dev *virt_dev,
+	bool read_only)
 {
 	int open_flags = 0;
 	struct file *fd;
@@ -615,7 +616,7 @@ static struct file *vdev_open_fd(const struct scst_vdisk_dev *virt_dev)
 
 	sBUG_ON(!virt_dev->filename);
 
-	if (virt_dev->dev->rd_only)
+	if (read_only)
 		open_flags |= O_RDONLY;
 	else
 		open_flags |= O_RDWR;
@@ -836,7 +837,7 @@ static int vdisk_attach(struct scst_device *dev)
 
 	virt_dev->dev = dev;
 
-	dev->rd_only = virt_dev->rd_only;
+	dev->dev_rd_only = virt_dev->rd_only;
 
 	if (!virt_dev->cdrom_empty) {
 		if (virt_dev->nullio)
@@ -913,7 +914,7 @@ static void vdisk_detach(struct scst_device *dev)
 	return;
 }
 
-static int vdisk_open_fd(struct scst_vdisk_dev *virt_dev)
+static int vdisk_open_fd(struct scst_vdisk_dev *virt_dev, bool read_only)
 {
 	int res;
 
@@ -922,7 +923,7 @@ static int vdisk_open_fd(struct scst_vdisk_dev *virt_dev)
 #endif
 	sBUG_ON(!virt_dev->filename);
 
-	virt_dev->fd = vdev_open_fd(virt_dev);
+	virt_dev->fd = vdev_open_fd(virt_dev, read_only);
 	if (IS_ERR(virt_dev->fd)) {
 		res = PTR_ERR(virt_dev->fd);
 		virt_dev->fd = NULL;
@@ -954,7 +955,7 @@ static int vdisk_attach_tgt(struct scst_tgt_dev *tgt_dev)
 		goto out;
 
 	if (!virt_dev->nullio && !virt_dev->cdrom_empty) {
-		res = vdisk_open_fd(virt_dev);
+		res = vdisk_open_fd(virt_dev, tgt_dev->tgt_dev_rd_only);
 		if (res != 0) {
 			virt_dev->tgt_dev_cnt--;
 			goto out;
@@ -2685,8 +2686,7 @@ static enum compl_status_e vdisk_exec_mode_sense(struct vdisk_cmd_params *p)
 	pcode = cmd->cdb[2] & 0x3f;
 	subpcode = cmd->cdb[3];
 	msense_6 = (MODE_SENSE == cmd->cdb[0]);
-	dev_spec = (virt_dev->dev->rd_only ||
-		     cmd->tgt_dev->acg_dev->rd_only) ? WP : 0;
+	dev_spec = cmd->tgt_dev->tgt_dev_rd_only ? WP : 0;
 
 	if (type != TYPE_ROM)
 		dev_spec |= DPOFUA;
@@ -2810,7 +2810,7 @@ out_not_sup:
 	goto out_put;
 }
 
-static int vdisk_set_wt(struct scst_vdisk_dev *virt_dev, int wt)
+static int vdisk_set_wt(struct scst_vdisk_dev *virt_dev, int wt, bool read_only)
 {
 	int res = 0;
 	struct file *fd;
@@ -2830,7 +2830,7 @@ static int vdisk_set_wt(struct scst_vdisk_dev *virt_dev, int wt)
 	 * to reopen fd.
 	 */
 
-	fd = vdev_open_fd(virt_dev);
+	fd = vdev_open_fd(virt_dev, read_only);
 	if (IS_ERR(fd)) {
 		PRINT_ERROR("filp_open(%s) returned an error %ld",
 			    virt_dev->filename, PTR_ERR(fd));
@@ -2934,8 +2934,8 @@ static enum compl_status_e vdisk_exec_mode_select(struct vdisk_cmd_params *p)
 				scst_set_invalid_field_in_parm_list(cmd, offset+1, 0);
 				goto out_put;
 			}
-			if (vdisk_set_wt(virt_dev,
-			      (address[offset + 2] & WCE) ? 0 : 1) != 0) {
+			if (vdisk_set_wt(virt_dev, (address[offset + 2] & WCE) ? 0 : 1,
+					cmd->tgt_dev->tgt_dev_rd_only) != 0) {
 				scst_set_busy(cmd);
 				goto out_put;
 			}
@@ -4176,7 +4176,8 @@ static void vdisk_task_mgmt_fn_done(struct scst_mgmt_cmd *mcmd,
 		else
 			dev->queue_alg = DEF_QUEUE_ALG;
 
-		rc = vdisk_set_wt(virt_dev, DEF_WRITE_THROUGH);
+		rc = vdisk_set_wt(virt_dev, DEF_WRITE_THROUGH,
+			tgt_dev->tgt_dev_rd_only);
 		if (rc != 0) {
 			PRINT_CRIT_ERROR("Unable to reset caching mode to %d",
 				DEF_WRITE_THROUGH);
@@ -4952,7 +4953,7 @@ static int vcdrom_change(struct scst_vdisk_dev *virt_dev,
 		if (res != 0)
 			goto out_free_fn;
 		if (virt_dev->tgt_dev_cnt > 0) {
-			res = vdisk_open_fd(virt_dev);
+			res = vdisk_open_fd(virt_dev, true);
 			if (res != 0)
 				goto out_free_fn;
 			sBUG_ON(!virt_dev->fd);
@@ -5609,7 +5610,7 @@ static int vdisk_read_proc(struct seq_file *seq, struct scst_dev_type *dev_type)
 			c += 3;
 		}
 		if (virt_dev->dev != NULL) {
-			if (virt_dev->dev->rd_only) {
+			if (virt_dev->dev->dev_rd_only) {
 				seq_printf(seq, "RO ");
 				c += 3;
 			}
diff --git a/scst/src/scst_lib.c b/scst/src/scst_lib.c
index 4efbf751d..4c192677e 100644
--- a/scst/src/scst_lib.c
+++ b/scst/src/scst_lib.c
@@ -2495,7 +2495,7 @@ retry_add:
 					sess_tgt_dev_list_entry) {
 				if ((tgt_dev->dev == acg_dev->dev) &&
 				    (tgt_dev->lun == acg_dev->lun) &&
-				    (tgt_dev->acg_dev->rd_only == acg_dev->rd_only)) {
+				    (tgt_dev->acg_dev->acg_dev_rd_only == acg_dev->acg_dev_rd_only)) {
 					TRACE_MGMT_DBG("sess %p: tgt_dev %p for "
 						"LUN %lld stays the same",
 						sess, tgt_dev,
@@ -3512,7 +3512,7 @@ int scst_acg_add_lun(struct scst_acg *acg, struct kobject *parent,
 		res = -ENOMEM;
 		goto out;
 	}
-	acg_dev->rd_only = read_only;
+	acg_dev->acg_dev_rd_only = read_only;
 
 	TRACE_DBG("Adding acg_dev %p to acg_dev_list and dev_acg_dev_list",
 		acg_dev);
@@ -4099,6 +4099,7 @@ static int scst_alloc_add_tgt_dev(struct scst_session *sess,
 	tgt_dev->dev = dev;
 	tgt_dev->lun = acg_dev->lun;
 	tgt_dev->acg_dev = acg_dev;
+	tgt_dev->tgt_dev_rd_only = acg_dev->acg_dev_rd_only || dev->dev_rd_only;
 	tgt_dev->sess = sess;
 	atomic_set(&tgt_dev->tgt_dev_cmd_count, 0);
 
@@ -4139,14 +4140,11 @@ static int scst_alloc_add_tgt_dev(struct scst_session *sess,
 	    dev->handler->dev_alloc_data_buf_atomic &&
 	    (sess->tgt->tgtt->preprocessing_done == NULL)) {
 		if (sess->tgt->tgtt->rdy_to_xfer_atomic)
-			__set_bit(SCST_TGT_DEV_AFTER_INIT_WR_ATOMIC,
-				&tgt_dev->tgt_dev_flags);
+			tgt_dev->tgt_dev_after_init_wr_atomic = 1;
 	}
 	if (dev->handler->dev_done_atomic &&
-	    sess->tgt->tgtt->xmit_response_atomic) {
-		__set_bit(SCST_TGT_DEV_AFTER_EXEC_ATOMIC,
-			&tgt_dev->tgt_dev_flags);
-	}
+	    sess->tgt->tgtt->xmit_response_atomic)
+		tgt_dev->tgt_dev_after_exec_atimic = 1;
 
 	sl = scst_set_sense(sense_buffer, sizeof(sense_buffer),
 		dev->d_sense, SCST_LOAD_SENSE(scst_sense_reset_UA));
diff --git a/scst/src/scst_mem.c b/scst/src/scst_mem.c
index a2841553d..ca36975ea 100644
--- a/scst/src/scst_mem.c
+++ b/scst/src/scst_mem.c
@@ -90,7 +90,7 @@ void scst_sgv_pool_use_norm(struct scst_tgt_dev *tgt_dev)
 {
 	tgt_dev->gfp_mask = __GFP_NOWARN;
 	tgt_dev->pool = sgv_norm_pool;
-	clear_bit(SCST_TGT_DEV_CLUST_POOL, &tgt_dev->tgt_dev_flags);
+	tgt_dev->tgt_dev_clust_pool = 0;
 }
 
 void scst_sgv_pool_use_norm_clust(struct scst_tgt_dev *tgt_dev)
@@ -98,7 +98,7 @@ void scst_sgv_pool_use_norm_clust(struct scst_tgt_dev *tgt_dev)
 	TRACE_MEM("%s", "Use clustering");
 	tgt_dev->gfp_mask = __GFP_NOWARN;
 	tgt_dev->pool = sgv_norm_clust_pool;
-	set_bit(SCST_TGT_DEV_CLUST_POOL, &tgt_dev->tgt_dev_flags);
+	tgt_dev->tgt_dev_clust_pool = 1;
 }
 
 void scst_sgv_pool_use_dma(struct scst_tgt_dev *tgt_dev)
@@ -106,7 +106,7 @@ void scst_sgv_pool_use_dma(struct scst_tgt_dev *tgt_dev)
 	TRACE_MEM("%s", "Use ISA DMA memory");
 	tgt_dev->gfp_mask = __GFP_NOWARN | GFP_DMA;
 	tgt_dev->pool = sgv_dma_pool;
-	clear_bit(SCST_TGT_DEV_CLUST_POOL, &tgt_dev->tgt_dev_flags);
+	tgt_dev->tgt_dev_clust_pool = 0;
 }
 
 /* Must be no locks */
diff --git a/scst/src/scst_proc.c b/scst/src/scst_proc.c
index 5013499c6..a451f516f 100644
--- a/scst/src/scst_proc.c
+++ b/scst/src/scst_proc.c
@@ -2532,7 +2532,7 @@ static int scst_groups_devices_show(struct seq_file *seq, void *v)
 		seq_printf(seq, "%-60s%-13lld%s\n",
 			       acg_dev->dev->virt_name,
 			       (long long unsigned int)acg_dev->lun,
-			       acg_dev->rd_only ? "RO" : "");
+			       acg_dev->acg_dev_rd_only ? "RO" : "");
 	}
 	mutex_unlock(&scst_mutex);
 
diff --git a/scst/src/scst_sysfs.c b/scst/src/scst_sysfs.c
index 802cb03d3..30ad1b569 100644
--- a/scst/src/scst_sysfs.c
+++ b/scst/src/scst_sysfs.c
@@ -3730,7 +3730,7 @@ static ssize_t scst_lun_rd_only_show(struct kobject *kobj,
 
 	acg_dev = container_of(kobj, struct scst_acg_dev, acg_dev_kobj);
 
-	if (acg_dev->rd_only || acg_dev->dev->rd_only)
+	if (acg_dev->acg_dev_rd_only || acg_dev->dev->dev_rd_only)
 		return sprintf(buf, "%d\n%s\n", 1, SCST_SYSFS_KEY_MARK);
 	else
 		return sprintf(buf, "%d\n", 0);
diff --git a/scst/src/scst_targ.c b/scst/src/scst_targ.c
index c2a3da00c..90c56ec82 100644
--- a/scst/src/scst_targ.c
+++ b/scst/src/scst_targ.c
@@ -345,8 +345,7 @@ static int scst_init_cmd(struct scst_cmd *cmd, enum scst_exec_context *context)
 		 */
 		BUILD_BUG_ON(SCST_DATA_UNKNOWN != 0);
 		if ((cmd->data_direction | cmd->expected_data_direction) & SCST_DATA_WRITE) {
-			if (!test_bit(SCST_TGT_DEV_AFTER_INIT_WR_ATOMIC,
-					&cmd->tgt_dev->tgt_dev_flags))
+			if (!cmd->tgt_dev->tgt_dev_after_init_wr_atomic)
 				*context = SCST_CONTEXT_THREAD;
 		} else
 			*context = SCST_CONTEXT_THREAD;
@@ -1712,8 +1711,7 @@ static inline enum scst_exec_context scst_optimize_post_exec_context(
 	if (((context == SCST_CONTEXT_SAME) && scst_cmd_atomic(cmd)) ||
 	    (context == SCST_CONTEXT_TASKLET) ||
 	    (context == SCST_CONTEXT_DIRECT_ATOMIC)) {
-		if (!test_bit(SCST_TGT_DEV_AFTER_EXEC_ATOMIC,
-				&cmd->tgt_dev->tgt_dev_flags))
+		if (!cmd->tgt_dev->tgt_dev_after_exec_atimic)
 			context = SCST_CONTEXT_THREAD;
 	}
 	return context;
@@ -2765,8 +2763,7 @@ static int scst_do_local_exec(struct scst_cmd *cmd)
 
 	/* Check READ_ONLY device status */
 	if ((cmd->op_flags & SCST_WRITE_MEDIUM) &&
-	    (tgt_dev->acg_dev->rd_only || cmd->dev->swp ||
-	     cmd->dev->rd_only)) {
+	    (tgt_dev->tgt_dev_rd_only || cmd->dev->swp)) {
 		PRINT_WARNING("Attempt of write access to read-only device: "
 			"initiator %s, LUN %lld, op %x",
 			cmd->sess->initiator_name, cmd->lun, cmd->cdb[0]);
@@ -3174,8 +3171,7 @@ static int scst_pre_dev_done(struct scst_cmd *cmd)
 		unsigned char type = cmd->dev->type;
 		if (unlikely((cmd->cdb[0] == MODE_SENSE ||
 			      cmd->cdb[0] == MODE_SENSE_10)) &&
-		    (cmd->tgt_dev->acg_dev->rd_only || cmd->dev->swp ||
-		     cmd->dev->rd_only) &&
+		    (cmd->tgt_dev->tgt_dev_rd_only || cmd->dev->swp) &&
 		    (type == TYPE_DISK ||
 		     type == TYPE_WORM ||
 		     type == TYPE_MOD ||