linux-kernel - Re: [PATCH] memcg: fix Bad page state after replace_page

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Message-ID: <alpine.LSU.2.00.1204241211050.18485@eggly.anvils>
Date:	Tue, 24 Apr 2012 12:13:26 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Johannes Weiner <hannes@...xchg.org>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Miklos Szeredi <mszeredi@...e.cz>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Michal Hocko <mhocko@...e.cz>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH] memcg: fix Bad page state after replace_page_cache

On Tue, 24 Apr 2012, Johannes Weiner wrote:
> From: Johannes Weiner <hannes@...xchg.org>
> Subject: [patch] mm: memcg: move pc lookup point to commit_charge()
> 
> None of the callsites actually need the page_cgroup descriptor
> themselves, so just pass the page and do the look up in there.
> 
> We already had two bugs (6568d4a 'mm: memcg: update the correct soft
> limit tree during migration' and 'memcg: fix Bad page state after
> replace_page_cache') where the passed page and pc were not referring
> to the same page frame.
> 
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

Excellent, thank you:
Acked-by: Hugh Dickins <hughd@...gle.com>

> ---
>  mm/memcontrol.c |   17 +++++------------
>  1 files changed, 5 insertions(+), 12 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 884e936..1a28dd8 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2461,10 +2461,10 @@ struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page)
>  static void __mem_cgroup_commit_charge(struct mem_cgroup *memcg,
>  				       struct page *page,
>  				       unsigned int nr_pages,
> -				       struct page_cgroup *pc,
>  				       enum charge_type ctype,
>  				       bool lrucare)
>  {
> +	struct page_cgroup *pc = lookup_page_cgroup(page);
>  	struct zone *uninitialized_var(zone);
>  	bool was_on_lru = false;
>  	bool anon;
> @@ -2701,7 +2701,6 @@ static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm,
>  {
>  	struct mem_cgroup *memcg = NULL;
>  	unsigned int nr_pages = 1;
> -	struct page_cgroup *pc;
>  	bool oom = true;
>  	int ret;
>  
> @@ -2715,11 +2714,10 @@ static int mem_cgroup_charge_common(struct page *page, struct mm_struct *mm,
>  		oom = false;
>  	}
>  
> -	pc = lookup_page_cgroup(page);
>  	ret = __mem_cgroup_try_charge(mm, gfp_mask, nr_pages, &memcg, oom);
>  	if (ret == -ENOMEM)
>  		return ret;
> -	__mem_cgroup_commit_charge(memcg, page, nr_pages, pc, ctype, false);
> +	__mem_cgroup_commit_charge(memcg, page, nr_pages, ctype, false);
>  	return 0;
>  }
>  
> @@ -2816,16 +2814,13 @@ static void
>  __mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *memcg,
>  					enum charge_type ctype)
>  {
> -	struct page_cgroup *pc;
> -
>  	if (mem_cgroup_disabled())
>  		return;
>  	if (!memcg)
>  		return;
>  	cgroup_exclude_rmdir(&memcg->css);
>  
> -	pc = lookup_page_cgroup(page);
> -	__mem_cgroup_commit_charge(memcg, page, 1, pc, ctype, true);
> +	__mem_cgroup_commit_charge(memcg, page, 1, ctype, true);
>  	/*
>  	 * Now swap is on-memory. This means this page may be
>  	 * counted both as mem and swap....double count.
> @@ -3254,14 +3249,13 @@ int mem_cgroup_prepare_migration(struct page *page,
>  	 * page. In the case new page is migrated but not remapped, new page's
>  	 * mapcount will be finally 0 and we call uncharge in end_migration().
>  	 */
> -	pc = lookup_page_cgroup(newpage);
>  	if (PageAnon(page))
>  		ctype = MEM_CGROUP_CHARGE_TYPE_MAPPED;
>  	else if (page_is_file_cache(page))
>  		ctype = MEM_CGROUP_CHARGE_TYPE_CACHE;
>  	else
>  		ctype = MEM_CGROUP_CHARGE_TYPE_SHMEM;
> -	__mem_cgroup_commit_charge(memcg, newpage, 1, pc, ctype, false);
> +	__mem_cgroup_commit_charge(memcg, newpage, 1, ctype, false);
>  	return ret;
>  }
>  
> @@ -3348,8 +3342,7 @@ void mem_cgroup_replace_page_cache(struct page *oldpage,
>  	 * the newpage may be on LRU(or pagevec for LRU) already. We lock
>  	 * LRU while we overwrite pc->mem_cgroup.
>  	 */
> -	pc = lookup_page_cgroup(newpage);
> -	__mem_cgroup_commit_charge(memcg, newpage, 1, pc, type, true);
> +	__mem_cgroup_commit_charge(memcg, newpage, 1, type, true);
>  }
>  
>  #ifdef CONFIG_DEBUG_VM
> -- 
> 1.7.7.6
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