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

[Su Yue <suy.fnst@cn.fujitsu.com>]

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.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.
> 

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 */
>>
> 
>