Re: [RFC] [PATCH 1/7 v2] memcg: remove unnecessary check in mem_cgroup_update_page_stat()

[Michal Hocko <mhocko@suse.cz>]

On Fri 13-01-12 17:32:27, KAMEZAWA Hiroyuki wrote:
> 
> From 788aebf15f3fa37940e0745cab72547e20683bf2 Mon Sep 17 00:00:00 2001
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Date: Thu, 12 Jan 2012 16:08:33 +0900
> Subject: [PATCH 1/7] memcg: remove unnecessary check in mem_cgroup_update_page_stat()
> 
> commit 10ea69f1182b removes move_lock_page_cgroup() in thp-split path.
> So, this PageTransHuge() check is unnecessary, too.

I do not see commit like that in the tree. I guess you meant
memcg: make mem_cgroup_split_huge_fixup() more efficient which is not
merged yet, right?

> 
> Note:
>  - considering when mem_cgroup_update_page_stat() is called,
>    there will be no race between split_huge_page() and update_page_stat().
>    All required locks are held in higher level.

We should never have THP page in this path in the first place. So why
not changing this to VM_BUG_ON(PageTransHuge).

> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> ---
>  mm/memcontrol.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 21ba356..08b988d 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1866,7 +1866,7 @@ void mem_cgroup_update_page_stat(struct page *page,
>  	if (unlikely(!memcg || !PageCgroupUsed(pc)))
>  		goto out;
>  	/* pc->mem_cgroup is unstable ? */
> -	if (unlikely(mem_cgroup_stealed(memcg)) || PageTransHuge(page)) {
> +	if (unlikely(mem_cgroup_stealed(memcg))) {
>  		/* take a lock against to access pc->mem_cgroup */
>  		move_lock_page_cgroup(pc, &flags);
>  		need_unlock = true;
> -- 
> 1.7.4.1
> 
> 
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-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic

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