diff --git a/scst/README b/scst/README
index 41bc0576a..b2fff1aef 100644
--- a/scst/README
+++ b/scst/README
@@ -1952,6 +1952,20 @@ context switch is natural for such potentially long operation as
 EXTENDED COPY.
 
 
+VMware and Ceph RBD space reclaim
+---------------------------------
+
+VMware with VMFS5 filesystem ignores UNMAP alignment, so if you use 4MB
+Ceph RBD objects and VMFS5, only some discards will reclaim RBD space
+due to 1MB discard not often hitting the tail of objects.
+
+Thus, to have efficient ESXi space reclamation with RBD and VMFS5, you are
+recommended to use 1 MB object size in Ceph.
+
+See https://sourceforge.net/p/scst/mailman/message/35287598 thread for
+details.
+
+
 Caching
 -------
 
diff --git a/scst/README_in-tree b/scst/README_in-tree
index 78e94401d..65053019d 100644
--- a/scst/README_in-tree
+++ b/scst/README_in-tree
@@ -1805,6 +1805,20 @@ context switch is natural for such potentially long operation as
 EXTENDED COPY.
 
 
+VMware and Ceph RBD space reclaim
+---------------------------------
+
+VMware with VMFS5 filesystem ignores UNMAP alignment, so if you use 4MB
+Ceph RBD objects and VMFS5, only some discards will reclaim RBD space
+due to 1MB discard not often hitting the tail of objects.
+
+Thus, to have efficient ESXi space reclamation with RBD and VMFS5, you are
+recommended to use 1 MB object size in Ceph.
+
+See https://sourceforge.net/p/scst/mailman/message/35287598 thread for
+details.
+
+
 Caching
 -------
 
diff --git a/scst/include/backport.h b/scst/include/backport.h
index c7c923eae..eec927283 100644
--- a/scst/include/backport.h
+++ b/scst/include/backport.h
@@ -678,4 +678,19 @@ static inline int scsi_bidi_cmnd(struct scsi_cmnd *cmd)
 }
 #endif
 
+#if (LINUX_VERSION_CODE >= KERNEL_VERSION(3, 9, 0)) && \
+    (LINUX_VERSION_CODE < KERNEL_VERSION(3, 16, 0))
+/**
+ * ktime_before - Compare if a ktime_t value is smaller than another one.
+ * @cmp1:	comparable1
+ * @cmp2:	comparable2
+ *
+ * Return: true if cmp1 happened before cmp2.
+ */
+static inline bool ktime_before(const ktime_t cmp1, const ktime_t cmp2)
+{
+	return ktime_compare(cmp1, cmp2) < 0;
+}
+#endif /* (LINUX_VERSION_CODE >= KERNEL_VERSION(3, 9, 0)) && (LINUX_VERSION_CODE < KERNEL_VERSION(3, 16, 0)) */
+
 #endif /* _SCST_BACKPORT_H_ */
diff --git a/scst/src/scst_main.c b/scst/src/scst_main.c
index b8affa4a8..81fb1a56e 100644
--- a/scst/src/scst_main.c
+++ b/scst/src/scst_main.c
@@ -121,7 +121,9 @@ unsigned long scst_trace_flag;
 
 unsigned long scst_flags;
 
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(3, 9, 0)
 unsigned long scst_poll_ns = SCST_DEF_POLL_NS;
+#endif
 
 int scst_max_tasklet_cmd = SCST_DEF_MAX_TASKLET_CMD;
 
diff --git a/scst/src/scst_priv.h b/scst/src/scst_priv.h
index 6f89563ba..a44a5837c 100644
--- a/scst/src/scst_priv.h
+++ b/scst/src/scst_priv.h
@@ -184,8 +184,10 @@ extern unsigned int scst_setup_id;
 #define SCST_DEF_MAX_TASKLET_CMD 10
 extern int scst_max_tasklet_cmd;
 
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(3, 9, 0)
 #define SCST_DEF_POLL_NS 0
 extern unsigned long scst_poll_ns;
+#endif
 
 extern spinlock_t scst_init_lock;
 extern struct list_head scst_init_cmd_list;
diff --git a/scst/src/scst_sysfs.c b/scst/src/scst_sysfs.c
index fa6c33313..d9871a3f9 100644
--- a/scst/src/scst_sysfs.c
+++ b/scst/src/scst_sysfs.c
@@ -7059,6 +7059,8 @@ static struct kobj_attribute scst_max_tasklet_cmd_attr =
 	__ATTR(max_tasklet_cmd, S_IRUGO | S_IWUSR, scst_max_tasklet_cmd_show,
 	       scst_max_tasklet_cmd_store);
 
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(3, 9, 0)
+
 static ssize_t scst_poll_us_show(struct kobject *kobj,
 				  struct kobj_attribute *attr, char *buf)
 {
@@ -7106,6 +7108,8 @@ static struct kobj_attribute scst_poll_us_attr =
 	__ATTR(poll_us, S_IRUGO | S_IWUSR, scst_poll_us_show,
 	       scst_poll_us_store);
 
+#endif /* LINUX_VERSION_CODE >= KERNEL_VERSION(3, 9, 0) */
+
 static ssize_t scst_suspend_show(struct kobject *kobj,
 				 struct kobj_attribute *attr, char *buf)
 {
@@ -7380,7 +7384,9 @@ static struct attribute *scst_sysfs_root_default_attrs[] = {
 	&scst_threads_attr.attr,
 	&scst_setup_id_attr.attr,
 	&scst_max_tasklet_cmd_attr.attr,
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(3, 9, 0)
 	&scst_poll_us_attr.attr,
+#endif
 	&scst_suspend_attr.attr,
 #if defined(CONFIG_SCST_DEBUG) || defined(CONFIG_SCST_TRACING)
 	&scst_main_trace_level_attr.attr,
diff --git a/scst/src/scst_targ.c b/scst/src/scst_targ.c
index 0f510b127..cbed2c8a8 100644
--- a/scst/src/scst_targ.c
+++ b/scst/src/scst_targ.c
@@ -5623,6 +5623,7 @@ again:
 			thr_locked = false;
 		}
 
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(3, 9, 0)
 		if (scst_poll_ns > 0) {
 			struct timespec ts;
 			ktime_t end, kt;
@@ -5655,6 +5656,7 @@ again:
 		}
 
 go:
+#endif
 		spin_lock_irq(&p_cmd_threads->cmd_list_lock);
 		spin_lock(&thr->thr_cmd_list_lock);
 	}