linux-ext4 - Re: [PATCH v3 28/49] dm zoned: dynamically allocate the dm-zoned-meta shrinker

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Date:   Thu, 27 Jul 2023 18:32:10 +0800
From:   Qi Zheng <zhengqi.arch@...edance.com>
To:     Damien Le Moal <dlemoal@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org,
        kvm@...r.kernel.org, xen-devel@...ts.xenproject.org,
        linux-erofs@...ts.ozlabs.org,
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        rcu@...r.kernel.org, netdev@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        dm-devel@...hat.com, linux-raid@...r.kernel.org,
        linux-bcache@...r.kernel.org,
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        linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
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        Muchun Song <songmuchun@...edance.com>,
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        muchun.song@...ux.dev
Subject: Re: [PATCH v3 28/49] dm zoned: dynamically allocate the dm-zoned-meta
 shrinker



On 2023/7/27 18:20, 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... So not adding that super simple

It also needs to be exported to the driver for use.

> helper is not exactly the best choice in my opinion.

Hm, either one is fine for me. If no one else objects, I can add this
helper. ;)

>