On 01/31/2018 04:06 PM, Nikolay Borisov wrote:
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 1a462ab85c49..4759e988b0df 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1100,6 +1100,8 @@ struct btrfs_fs_info {
spinlock_t ref_verify_lock;
struct rb_root block_tree;
#endif
+ /* Policy to balance read across mirrored devices */
+ int read_mirror_policy;
make that member enum btrfs_read_mirror_type
yep. Will do.
::
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index a61715677b67..39ba59832f38 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -5269,7 +5269,13 @@ static int find_live_mirror(struct btrfs_fs_info *fs_info,
else
num = map->num_stripes;
- optimal = first + current->pid % num;
+ switch(fs_info->read_mirror_policy) {
+ case BTRFS_READ_MIRROR_DEFAULT:
+ case BTRFS_READ_MIRROR_BY_PID:
+ default:
+ optimal = first + current->pid % num;
+ break;
+ }
Why not factor out this code in a separate function with descriptive
name and some documentation. It seems you have plans how to extend this
mechanism further so let's try and make it maintainable from the get-go.
This is in fact restoring the original design, will add comments.
In the long term we may have up couple of more choices (like LBA),
will move it to a function.
Thanks, Anand
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