netdev - Re: [PATCH v2 03/47] mm: shrinker: add infrastructure for dynamically allocating shrinker

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Message-ID: <0caf10e8-e54b-3c1b-7df5-d95adc757ba7@bytedance.com>
Date: Wed, 26 Jul 2023 17:20:49 +0800
From: Qi Zheng <zhengqi.arch@...edance.com>
To: Dave Chinner <david@...morbit.com>
Cc: akpm@...ux-foundation.org, tkhai@...ru, vbabka@...e.cz,
 roman.gushchin@...ux.dev, djwong@...nel.org, brauner@...nel.org,
 paulmck@...nel.org, tytso@....edu, steven.price@....com, cel@...nel.org,
 senozhatsky@...omium.org, yujie.liu@...el.com, gregkh@...uxfoundation.org,
 muchun.song@...ux.dev, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
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 linux-erofs@...ts.ozlabs.org, linux-f2fs-devel@...ts.sourceforge.net,
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Subject: Re: [PATCH v2 03/47] mm: shrinker: add infrastructure for dynamically
 allocating shrinker

Hi Dave,

On 2023/7/26 15:26, Dave Chinner wrote:
> On Mon, Jul 24, 2023 at 05:43:10PM +0800, Qi Zheng wrote:
>> Currently, the shrinker instances can be divided into the following three
>> types:
>>
>> a) global shrinker instance statically defined in the kernel, such as
>>     workingset_shadow_shrinker.
>>
>> b) global shrinker instance statically defined in the kernel modules, such
>>     as mmu_shrinker in x86.
>>
>> c) shrinker instance embedded in other structures.
>>
>> For case a, the memory of shrinker instance is never freed. For case b,
>> the memory of shrinker instance will be freed after synchronize_rcu() when
>> the module is unloaded. For case c, the memory of shrinker instance will
>> be freed along with the structure it is embedded in.
>>
>> In preparation for implementing lockless slab shrink, we need to
>> dynamically allocate those shrinker instances in case c, then the memory
>> can be dynamically freed alone by calling kfree_rcu().
>>
>> So this commit adds the following new APIs for dynamically allocating
>> shrinker, and add a private_data field to struct shrinker to record and
>> get the original embedded structure.
>>
>> 1. shrinker_alloc()
>>
>> Used to allocate shrinker instance itself and related memory, it will
>> return a pointer to the shrinker instance on success and NULL on failure.
>>
>> 2. shrinker_free_non_registered()
>>
>> Used to destroy the non-registered shrinker instance.
> 
> This is a bit nasty
> 
>>
>> 3. shrinker_register()
>>
>> Used to register the shrinker instance, which is same as the current
>> register_shrinker_prepared().
>>
>> 4. shrinker_unregister()
> 
> rename this "shrinker_free()" and key the two different freeing
> cases on the SHRINKER_REGISTERED bit rather than mostly duplicating
> the two.

OK, will do in the next version.

> 
> void shrinker_free(struct shrinker *shrinker)
> {
> 	struct dentry *debugfs_entry = NULL;
> 	int debugfs_id;
> 
> 	if (!shrinker)
> 		return;
> 
> 	down_write(&shrinker_rwsem);
> 	if (shrinker->flags & SHRINKER_REGISTERED) {
> 		list_del(&shrinker->list);
> 		debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id);
> 	} else if (IS_ENABLED(CONFIG_SHRINKER_DEBUG)) {
> 		kfree_const(shrinker->name);
> 	}
> 
> 	if (shrinker->flags & SHRINKER_MEMCG_AWARE)
> 		unregister_memcg_shrinker(shrinker);
> 	up_write(&shrinker_rwsem);
> 
> 	if (debugfs_entry)
> 		shrinker_debugfs_remove(debugfs_entry, debugfs_id);
> 
> 	kfree(shrinker->nr_deferred);
> 	kfree(shrinker);
> }
> EXPORT_SYMBOL_GPL(shrinker_free);

Ah, I will change all new APIs to use EXPORT_SYMBOL_GPL().

Thanks,
Qi

>