diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 43e515939b9c..8479ab037812 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -448,6 +448,7 @@ struct btrfs_discard_ctl {
 	struct btrfs_block_group_cache *cache;
 	struct list_head discard_list[BTRFS_NR_DISCARD_LISTS];
 	atomic_t discard_extents;
+	atomic64_t discardable_bytes;
 };
 
 /* delayed seq elem */
diff --git a/fs/btrfs/discard.c b/fs/btrfs/discard.c
index 0544eb6717d4..75a2ff14b3c0 100644
--- a/fs/btrfs/discard.c
+++ b/fs/btrfs/discard.c
@@ -300,6 +300,7 @@ void btrfs_discard_init(struct btrfs_fs_info *fs_info)
 		 INIT_LIST_HEAD(&discard_ctl->discard_list[i]);
 
 	atomic_set(&discard_ctl->discard_extents, 0);
+	atomic64_set(&discard_ctl->discardable_bytes, 0);
 }
 
 void btrfs_discard_cleanup(struct btrfs_fs_info *fs_info)
diff --git a/fs/btrfs/discard.h b/fs/btrfs/discard.h
index 85939d62521e..d55a9a9f8ad8 100644
--- a/fs/btrfs/discard.h
+++ b/fs/btrfs/discard.h
@@ -77,6 +77,7 @@ void btrfs_discard_update_discardable(struct btrfs_block_group_cache *cache,
 {
 	struct btrfs_discard_ctl *discard_ctl;
 	s32 extents_delta;
+	s64 bytes_delta;
 
 	if (!cache || !btrfs_test_opt(cache->fs_info, DISCARD_ASYNC))
 		return;
@@ -88,6 +89,12 @@ void btrfs_discard_update_discardable(struct btrfs_block_group_cache *cache,
 		atomic_add(extents_delta, &discard_ctl->discard_extents);
 		ctl->discard_extents[1] = ctl->discard_extents[0];
 	}
+
+	bytes_delta = ctl->discardable_bytes[0] - ctl->discardable_bytes[1];
+	if (bytes_delta) {
+		atomic64_add(bytes_delta, &discard_ctl->discardable_bytes);
+		ctl->discardable_bytes[1] = ctl->discardable_bytes[0];
+	}
 }
 
 #endif
diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
index 6c2bebfd206f..54f3c8325858 100644
--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -814,6 +814,7 @@ static int __load_free_space_cache(struct btrfs_root *root, struct inode *inode,
 			goto free_cache;
 		e->bitmap_extents = count_bitmap_extents(ctl, e);
 		ctl->discard_extents[0] += e->bitmap_extents;
+		ctl->discardable_bytes[0] += e->bytes;
 	}
 
 	io_ctl_drop_pages(&io_ctl);
@@ -1636,8 +1637,10 @@ __unlink_free_space(struct btrfs_free_space_ctl *ctl,
 	rb_erase(&info->offset_index, &ctl->free_space_offset);
 	ctl->free_extents--;
 
-	if (!info->bitmap && !btrfs_free_space_trimmed(info))
+	if (!info->bitmap && !btrfs_free_space_trimmed(info)) {
 		ctl->discard_extents[0]--;
+		ctl->discardable_bytes[0] -= info->bytes;
+	}
 }
 
 static void unlink_free_space(struct btrfs_free_space_ctl *ctl,
@@ -1658,8 +1661,10 @@ static int link_free_space(struct btrfs_free_space_ctl *ctl,
 	if (ret)
 		return ret;
 
-	if (!info->bitmap && !btrfs_free_space_trimmed(info))
+	if (!info->bitmap && !btrfs_free_space_trimmed(info)) {
 		ctl->discard_extents[0]++;
+		ctl->discardable_bytes[0] += info->bytes;
+	}
 
 	ctl->free_space += info->bytes;
 	ctl->free_extents++;
@@ -1738,8 +1743,10 @@ static inline void __bitmap_clear_bits(struct btrfs_free_space_ctl *ctl,
 		extent_delta++;
 
 	info->bitmap_extents += extent_delta;
-	if (!btrfs_free_space_trimmed(info))
+	if (!btrfs_free_space_trimmed(info)) {
 		ctl->discard_extents[0] += extent_delta;
+		ctl->discardable_bytes[0] -= bytes;
+	}
 }
 
 static void bitmap_clear_bits(struct btrfs_free_space_ctl *ctl,
@@ -1774,8 +1781,10 @@ static void bitmap_set_bits(struct btrfs_free_space_ctl *ctl,
 		extent_delta--;
 
 	info->bitmap_extents += extent_delta;
-	if (!btrfs_free_space_trimmed(info))
+	if (!btrfs_free_space_trimmed(info)) {
 		ctl->discard_extents[0] += extent_delta;
+		ctl->discardable_bytes[0] += bytes;
+	}
 }
 
 /*
@@ -2042,8 +2051,10 @@ static u64 add_bytes_to_bitmap(struct btrfs_free_space_ctl *ctl,
 	u64 end;
 
 	if (!(flags & BTRFS_FSC_TRIMMED)) {
-		if (btrfs_free_space_trimmed(info))
+		if (btrfs_free_space_trimmed(info)) {
 			ctl->discard_extents[0] += info->bitmap_extents;
+			ctl->discardable_bytes[0] += info->bytes;
+		}
 		info->flags &= ~(BTRFS_FSC_TRIMMED | BTRFS_FSC_TRIMMING_BITMAP);
 	}
 
@@ -2657,15 +2668,19 @@ __btrfs_return_cluster_to_free_space(
 		bitmap = (entry->bitmap != NULL);
 		if (!bitmap) {
 			/* merging treats extents as if they were new */
-			if (!btrfs_free_space_trimmed(entry))
+			if (!btrfs_free_space_trimmed(entry)) {
 				ctl->discard_extents[0]--;
+				ctl->discardable_bytes[0] -= entry->bytes;
+			}
 
 			try_merge_free_space(ctl, entry, false);
 			steal_from_bitmap(ctl, entry, false);
 
 			/* as we insert directly, update these statistics */
-			if (!btrfs_free_space_trimmed(entry))
+			if (!btrfs_free_space_trimmed(entry)) {
 				ctl->discard_extents[0]++;
+				ctl->discardable_bytes[0] += entry->bytes;
+			}
 		}
 		tree_insert_offset(&ctl->free_space_offset,
 				   entry->offset, &entry->offset_index, bitmap);
@@ -2950,6 +2965,8 @@ u64 btrfs_alloc_from_cluster(struct btrfs_block_group_cache *block_group,
 	spin_lock(&ctl->tree_lock);
 
 	ctl->free_space -= bytes;
+	if (!entry->bitmap && !btrfs_free_space_trimmed(entry))
+		ctl->discardable_bytes[0] -= bytes;
 	if (entry->bytes == 0) {
 		ctl->free_extents--;
 		if (entry->bitmap) {
@@ -3467,6 +3484,7 @@ static void end_trimming_bitmap(struct btrfs_free_space_ctl *ctl,
 		entry->flags |= BTRFS_FSC_TRIMMED;
 		entry->flags &= ~BTRFS_FSC_TRIMMING_BITMAP;
 		ctl->discard_extents[0] -= entry->bitmap_extents;
+		ctl->discardable_bytes[0] -= entry->bytes;
 	}
 }
 
diff --git a/fs/btrfs/free-space-cache.h b/fs/btrfs/free-space-cache.h
index 855f42dc15cd..c5cce44b03af 100644
--- a/fs/btrfs/free-space-cache.h
+++ b/fs/btrfs/free-space-cache.h
@@ -41,6 +41,7 @@ struct btrfs_free_space_ctl {
 	int unit;
 	u64 start;
 	s32 discard_extents[2];
+	s64 discardable_bytes[2];
 	const struct btrfs_free_space_op *op;
 	void *private;
 	struct mutex cache_writeout_mutex;
diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
index 14c6910128f1..a2852706ec6c 100644
--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c
@@ -482,8 +482,20 @@ static ssize_t btrfs_discard_extents_show(struct kobject *kobj,
 }
 BTRFS_ATTR(discard, discard_extents, btrfs_discard_extents_show);
 
+static ssize_t btrfs_discardable_bytes_show(struct kobject *kobj,
+					struct kobj_attribute *a,
+					char *buf)
+{
+	struct btrfs_fs_info *fs_info = to_fs_info(kobj->parent);
+
+	return snprintf(buf, PAGE_SIZE, "%lld\n",
+			atomic64_read(&fs_info->discard_ctl.discardable_bytes));
+}
+BTRFS_ATTR(discard, discardable_bytes, btrfs_discardable_bytes_show);
+
 static const struct attribute *discard_attrs[] = {
 	BTRFS_ATTR_PTR(discard, discard_extents),
+	BTRFS_ATTR_PTR(discard, discardable_bytes),
 	NULL,
 };
 
