[PATCH 3/4] btrfs: tier-aware mirror path select

[wangyugui <wangyugui@e16-tech.com>]

This feature help the read performance, so it is enabled even if tier=off.

Signed-off-by: wangyugui <wangyugui@e16-tech.com>
---
 fs/btrfs/volumes.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 2a422ac..b65f916 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -5568,6 +5568,11 @@ static int find_live_mirror(struct btrfs_fs_info *fs_info,
 	int tolerance;
 	struct btrfs_device *srcdev;
 
+	/* tier-aware even if tier=off */
+	int top_tier_num_stripes = 0;
+	int top_tier_stripe_idxs[4]; /* RAID1C4 */
+	u8 top_tier_score = 0;
+
 	ASSERT((map->type &
 		 (BTRFS_BLOCK_GROUP_RAID1_MASK | BTRFS_BLOCK_GROUP_RAID10)));
 
@@ -5576,7 +5581,21 @@ static int find_live_mirror(struct btrfs_fs_info *fs_info,
 	else
 		num_stripes = map->num_stripes;
 
-	preferred_mirror = first + current->pid % num_stripes;
+	for (i = 0; i < num_stripes; ++i)
+	{
+		if (map->stripes[i].dev->tier_score > top_tier_score)
+		{
+			top_tier_score = map->stripes[i].dev->tier_score;
+			top_tier_stripe_idxs[0] = i;
+			top_tier_num_stripes = 1;
+		}
+		else if (map->stripes[i].dev->tier_score == top_tier_score)
+		{
+			top_tier_stripe_idxs[top_tier_num_stripes] = i;
+			top_tier_num_stripes++;
+		}
+	}
+	preferred_mirror = first + top_tier_stripe_idxs[current->pid % top_tier_num_stripes];
 
 	if (dev_replace_is_ongoing &&
 	    fs_info->dev_replace.cont_reading_from_srcdev_mode ==
-- 
2.29.1