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

[Qi Zheng]

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

>