linux-kernel - Re: [PATCH] mm: memcontrol: Don't css_get() on root_mem_cgroup in get_mem_cgroup_from

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <ZSlRcQ3JoPLFRBec@dhcp22.suse.cz>
Date:   Fri, 13 Oct 2023 16:17:21 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Waiman Long <longman@...hat.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Shakeel Butt <shakeelb@...gle.com>,
        Muchun Song <muchun.song@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH] mm: memcontrol: Don't css_get() on root_mem_cgroup in
 get_mem_cgroup_from_mm()

On Thu 12-10-23 12:15:04, Waiman Long wrote:
> As reference counting in the root memcg is disabled, there is no need
> to get a reference if root memcg is to be returned.

Does this give any measurable wins?
 
> Signed-off-by: Waiman Long <longman@...hat.com>
> ---
>  mm/memcontrol.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 5b009b233ab8..2b3864194042 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1060,8 +1060,10 @@ struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm)
>  	rcu_read_lock();
>  	do {
>  		memcg = mem_cgroup_from_task(rcu_dereference(mm->owner));
> -		if (unlikely(!memcg))
> +		if (unlikely(!memcg)) {
>  			memcg = root_mem_cgroup;
> +			break;
> +		}
>  	} while (!css_tryget(&memcg->css));
>  	rcu_read_unlock();
>  	return memcg;
> -- 
> 2.39.3

-- 
Michal Hocko
SUSE Labs