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.

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);

-- 
Dave Chinner
david@fromorbit.com