Re: [PATCH v2] btrfs: zoned: use greedy gc for auto reclaim

[Nikolay Borisov <nborisov@suse.com>]

On 13.10.21 г. 16:52, David Sterba wrote:
> On Tue, Oct 12, 2021 at 04:56:01PM +0300, Nikolay Borisov wrote:
>> On 12.10.21 г. 15:37, Johannes Thumshirn wrote:
>>> Currently auto reclaim of unusable zones reclaims the block-groups in the
>>> order they have been added to the reclaim list.
>>>
>>> Change this to a greedy algorithm by sorting the list so we have the
>>> block-groups with the least amount of valid bytes reclaimed first.
>>>
>>> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
>>>
>>> ---
>>> Changes since v1:
>>> -  Changed list_sort() comparator to 'boolean' style
>>>
>>> Changes since RFC:
>>> - Updated the patch description
>>> - Don't sort the list under the spin_lock (David)
>>
>> <snip>
>>
>>
>>> @@ -1510,17 +1528,20 @@ void btrfs_reclaim_bgs_work(struct work_struct *work)
>>>  	}
>>>  
>>>  	spin_lock(&fs_info->unused_bgs_lock);
>>> -	while (!list_empty(&fs_info->reclaim_bgs)) {
>>> +	list_splice_init(&fs_info->reclaim_bgs, &reclaim_list);
>>> +	spin_unlock(&fs_info->unused_bgs_lock);
>>> +
>>> +	list_sort(NULL, &reclaim_list, reclaim_bgs_cmp);
>>> +	while (!list_empty(&reclaim_list)) {
>>
>> Nit: Now that you've switched to a local reclaim_list you can convert
>> the while to a list_for_each_entry_safe, since it's guaranteed that new
>> entries can't be added while you are iterating the list, which is
>> generally the reason why a while() is preferred to one of the iteration
>> helpers.
> 
> Like the following? I'll fold it in if yes:

Yes