[RFC PATCH 01/17] btrfs: priority alloc: prepare of priority aware allocator

[Su Yue]

To implement priority aware allocator, this patch:
Introduces struct btrfs_priority_tree which contains block groups
in same level.
Adds member priority to struct btrfs_block_group_cache and pointer
points to the priority tree it's located.

Adds member priority_trees to struct btrfs_space_info to represents
priority trees in different raid types.

Signed-off-by: Su Yue <suy.f...@cn.fujitsu.com>
---
 fs/btrfs/ctree.h | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index e62824cae00a..5c4651d8a524 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -437,6 +437,8 @@ struct btrfs_space_info {
        struct rw_semaphore groups_sem;
        /* for block groups in our same type */
        struct list_head block_groups[BTRFS_NR_RAID_TYPES];
+       /* for priority trees in our same type */
+       struct rb_root priority_trees[BTRFS_NR_RAID_TYPES];
        wait_queue_head_t wait;
 
        struct kobject kobj;
@@ -558,6 +560,21 @@ struct btrfs_full_stripe_locks_tree {
        struct mutex lock;
 };
 
+/*
+ * Tree to record all block_groups in same priority level.
+ * Only used in priority aware allocator.
+ */
+struct btrfs_priority_tree {
+       /* protected by groups_sem */
+       struct rb_root block_groups;
+       struct rw_semaphore groups_sem;
+
+       /* for different level priority trees in same index*/
+       struct rb_node node;
+
+       int level;
+};
+
 struct btrfs_block_group_cache {
        struct btrfs_key key;
        struct btrfs_block_group_item item;
@@ -571,6 +588,8 @@ struct btrfs_block_group_cache {
        u64 flags;
        u64 cache_generation;
 
+       /* It's used only when priority aware allocator is enabled. */
+       long priority;
        /*
         * If the free space extent count exceeds this number, convert the block
         * group to bitmaps.
@@ -616,6 +635,9 @@ struct btrfs_block_group_cache {
        /* for block groups in the same raid type */
        struct list_head list;
 
+       /* for block groups in the same priority level */
+       struct rb_node node;
+
        /* usage count */
        atomic_t count;
 
@@ -670,6 +692,8 @@ struct btrfs_block_group_cache {
 
        /* Record locked full stripes for RAID5/6 block group */
        struct btrfs_full_stripe_locks_tree full_stripe_locks_root;
+
+       struct btrfs_priority_tree *priority_tree;
 };
 
 /* delayed seq elem */
-- 
2.19.1