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

[Su Yue]

On 11/28/18 4:24 PM, Nikolay Borisov wrote:

On 28.11.18 г. 5:11 ч., Su Yue wrote:

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;

Do you ever expect the level to be a negative number? If not then use
u8/u32 depending on the range of levels you expect.

Indeed, level is not expected to be negative. u8 is more proper.

+};
+
  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;

What's the range of priorities you are expecting, wouldn't an u8 be
sufficient, that gives us 256 priorities?

The 6th patch introduces three special priorities. That's what I called
dirty codes.

Thanks,
Su

        /*
         * 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 */