btrfs: only keep track of data extents for async discard

As mentioned earlier, discarding data can be done either by issuing an explicit discard or implicitly by reusing the LBA. Metadata block_groups see much more frequent reuse due to well it being metadata. So instead of explicitly discarding metadata block_groups, just leave them be and let the latter implicit discarding be done for them. For mixed block_groups, block_groups which contain both metadata and data, we let them be as higher fragmentation is expected. Reviewed-by: Josef Bacik <[email protected]> Signed-off-by: Dennis Zhou <[email protected]> Reviewed-by: David Sterba <[email protected]> Signed-off-by: David Sterba <[email protected]>
amarioguy · Jan 20, 2020 · 5cb0724 · 5cb0724
1 parent 7fe6d45
commit 5cb0724
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Showing 2 changed files with 21 additions and 2 deletions.
diff --git a/fs/btrfs/block-group.h b/fs/btrfs/block-group.h
@@ -182,6 +182,17 @@ static inline u64 btrfs_block_group_end(struct btrfs_block_group *block_group)
 	return (block_group->start + block_group->length);
 }
 
+static inline bool btrfs_is_block_group_data_only(
+					struct btrfs_block_group *block_group)
+{
+	/*
+	 * In mixed mode the fragmentation is expected to be high, lowering the
+	 * efficiency, so only proper data block groups are considered.
+	 */
+	return (block_group->flags & BTRFS_BLOCK_GROUP_DATA) &&
+	       !(block_group->flags & BTRFS_BLOCK_GROUP_METADATA);
+}
+
 #ifdef CONFIG_BTRFS_DEBUG
 static inline int btrfs_should_fragment_free_space(
 		struct btrfs_block_group *block_group)

diff --git a/fs/btrfs/discard.c b/fs/btrfs/discard.c
@@ -57,6 +57,9 @@ static void __add_to_discard_list(struct btrfs_discard_ctl *discard_ctl,
 static void add_to_discard_list(struct btrfs_discard_ctl *discard_ctl,
 				struct btrfs_block_group *block_group)
 {
+	if (!btrfs_is_block_group_data_only(block_group))
+		return;
+
 	spin_lock(&discard_ctl->lock);
 	__add_to_discard_list(discard_ctl, block_group);
 	spin_unlock(&discard_ctl->lock);
@@ -169,7 +172,10 @@ static struct btrfs_block_group *peek_discard_list(
 	if (block_group && now > block_group->discard_eligible_time) {
 		if (block_group->discard_index == BTRFS_DISCARD_INDEX_UNUSED &&
 		    block_group->used != 0) {
-			__add_to_discard_list(discard_ctl, block_group);
+			if (btrfs_is_block_group_data_only(block_group))
+				__add_to_discard_list(discard_ctl, block_group);
+			else
+				list_del_init(&block_group->discard_list);
 			goto again;
 		}
 		if (block_group->discard_state == BTRFS_DISCARD_RESET_CURSOR) {
@@ -507,7 +513,9 @@ void btrfs_discard_update_discardable(struct btrfs_block_group *block_group,
 	s32 extents_delta;
 	s64 bytes_delta;
 
-	if (!block_group || !btrfs_test_opt(block_group->fs_info, DISCARD_ASYNC))
+	if (!block_group ||
+	    !btrfs_test_opt(block_group->fs_info, DISCARD_ASYNC) ||
+	    !btrfs_is_block_group_data_only(block_group))
 		return;
 
 	discard_ctl = &block_group->fs_info->discard_ctl;