linux-kernel - Re: [PATCH 2/3] mm, memcg: Remove obsolete memcg_free

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Message-ID: <YVehP18mCcsXmFy1@carbon.dhcp.thefacebook.com>
Date:   Fri, 1 Oct 2021 17:01:03 -0700
From:   Roman Gushchin <guro@...com>
To:     Waiman Long <longman@...hat.com>
CC:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        <linux-kernel@...r.kernel.org>, <cgroups@...r.kernel.org>,
        <linux-mm@...ck.org>, Shakeel Butt <shakeelb@...gle.com>,
        Muchun Song <songmuchun@...edance.com>
Subject: Re: [PATCH 2/3] mm, memcg: Remove obsolete memcg_free_kmem()

On Fri, Oct 01, 2021 at 03:09:37PM -0400, Waiman Long wrote:
> Since commit d648bcc7fe65 ("mm: kmem: make memcg_kmem_enabled()
> irreversible"), the only thing memcg_free_kmem() does is to call
> memcg_offline_kmem() when the memcg is still online. However,
> memcg_offline_kmem() is only called from mem_cgroup_css_free() which
> cannot be reached if the memcg hasn't been offlined first.

Hm, is it true? What if online_css() fails?

> As this
> function now serves no purpose, we should just remove it.

It looks like we can just use memcg_offline_kmem() instead of
memcg_free_kmem().

Thanks!

> 
> Signed-off-by: Waiman Long <longman@...hat.com>
> ---
>  mm/memcontrol.c | 11 -----------
>  1 file changed, 11 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 4568363062c1..8177f253a127 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3673,13 +3673,6 @@ static void memcg_offline_kmem(struct mem_cgroup *memcg)
>  
>  	memcg_free_cache_id(kmemcg_id);
>  }
> -
> -static void memcg_free_kmem(struct mem_cgroup *memcg)
> -{
> -	/* css_alloc() failed, offlining didn't happen */
> -	if (unlikely(memcg->kmem_state == KMEM_ONLINE))
> -		memcg_offline_kmem(memcg);
> -}
>  #else
>  static int memcg_online_kmem(struct mem_cgroup *memcg)
>  {
> @@ -3688,9 +3681,6 @@ static int memcg_online_kmem(struct mem_cgroup *memcg)
>  static void memcg_offline_kmem(struct mem_cgroup *memcg)
>  {
>  }
> -static void memcg_free_kmem(struct mem_cgroup *memcg)
> -{
> -}
>  #endif /* CONFIG_MEMCG_KMEM */
>  
>  static int memcg_update_kmem_max(struct mem_cgroup *memcg,
> @@ -5325,7 +5315,6 @@ static void mem_cgroup_css_free(struct cgroup_subsys_state *css)
>  	cancel_work_sync(&memcg->high_work);
>  	mem_cgroup_remove_from_trees(memcg);
>  	free_shrinker_info(memcg);
> -	memcg_free_kmem(memcg);
>  	mem_cgroup_free(memcg);
>  }
>  
> -- 
> 2.18.1
>