Re: [PATCH v3 28/49] dm zoned: dynamically allocate the dm-zoned-meta shrinker

[Damien Le Moal <dlemoal@xxxxxxxxxx>]

On 7/28/23 07:59, Dave Chinner wrote:
> On Thu, Jul 27, 2023 at 07:20:46PM +0900, Damien Le Moal wrote:
>> On 7/27/23 17:55, Qi Zheng wrote:
>>>>>           goto err;
>>>>>       }
>>>>>   +    zmd->mblk_shrinker->count_objects = dmz_mblock_shrinker_count;
>>>>> +    zmd->mblk_shrinker->scan_objects = dmz_mblock_shrinker_scan;
>>>>> +    zmd->mblk_shrinker->seeks = DEFAULT_SEEKS;
>>>>> +    zmd->mblk_shrinker->private_data = zmd;
>>>>> +
>>>>> +    shrinker_register(zmd->mblk_shrinker);
>>>>
>>>> I fail to see how this new shrinker API is better... Why isn't there a
>>>> shrinker_alloc_and_register() function ? That would avoid adding all this 
>>>> code
>>>> all over the place as the new API call would be very similar to the current
>>>> shrinker_register() call with static allocation.
>>>
>>> In some registration scenarios, memory needs to be allocated in advance.
>>> So we continue to use the previous prealloc/register_prepared()
>>> algorithm. The shrinker_alloc_and_register() is just a helper function
>>> that combines the two, and this increases the number of APIs that
>>> shrinker exposes to the outside, so I choose not to add this helper.
>>
>> And that results in more code in many places instead of less code + a simple
>> inline helper in the shrinker header file...
> 
> It's not just a "simple helper" - it's a function that has to take 6
> or 7 parameters with a return value that must be checked and
> handled.
> 
> This was done in the first versions of the patch set - the amount of
> code in each caller does not go down and, IMO, was much harder to
> read and determine "this is obviously correct" that what we have
> now.
> 
>> So not adding that super simple
>> helper is not exactly the best choice in my opinion.
> 
> Each to their own - I much prefer the existing style/API over having
> to go look up a helper function every time I want to check some
> random shrinker has been set up correctly....

OK. All fair points.


-- 
Damien Le Moal
Western Digital Research