Re: [PATCH v7 06/12] mm: multigenerational LRU: exploit locality in rmap

[Yu Zhao <yuzhao@google.com>]

On Tue, Feb 08, 2022 at 01:18:56AM -0700, Yu Zhao wrote:

<snipped>

> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index b72d75141e12..51c9bc8e965d 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -436,6 +436,7 @@ static inline struct obj_cgroup *__folio_objcg(struct folio *folio)
>   * - LRU isolation
>   * - lock_page_memcg()
>   * - exclusive reference
> + * - mem_cgroup_trylock_pages()
>   *
>   * For a kmem folio a caller should hold an rcu read lock to protect memcg
>   * associated with a kmem folio from being released.
> @@ -497,6 +498,7 @@ static inline struct mem_cgroup *folio_memcg_rcu(struct folio *folio)
>   * - LRU isolation
>   * - lock_page_memcg()
>   * - exclusive reference
> + * - mem_cgroup_trylock_pages()
>   *
>   * For a kmem page a caller should hold an rcu read lock to protect memcg
>   * associated with a kmem page from being released.
> @@ -934,6 +936,23 @@ void unlock_page_memcg(struct page *page);
>  
>  void __mod_memcg_state(struct mem_cgroup *memcg, int idx, int val);
>  
> +/* try to stablize folio_memcg() for all the pages in a memcg */
> +static inline bool mem_cgroup_trylock_pages(struct mem_cgroup *memcg)
> +{
> +	rcu_read_lock();
> +
> +	if (mem_cgroup_disabled() || !atomic_read(&memcg->moving_account))
> +		return true;
> +
> +	rcu_read_unlock();
> +	return false;
> +}
> +
> +static inline void mem_cgroup_unlock_pages(void)
> +{
> +	rcu_read_unlock();
> +}

Replaced the open-coded folio_memcg() lock with a new function
mem_cgroup_trylock_pages() as requested here:
https://lore.kernel.org/linux-mm/YeATr%2F%2FU6XD87fWF@dhcp22.suse.cz/

<snipped>