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

[Nikolay Borisov <nborisov@suse.com>]

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.fnst@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.

> +};
> +
>  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?

>  	/*
>  	 * 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 */
>