linux-kernel - Re: [PATCH 2/4] memcg: set page->mapping NULL before uncharge

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Message-Id: <20080929203912.41327fd0.nishimura@mxp.nes.nec.co.jp>
Date:	Mon, 29 Sep 2008 20:39:12 +0900
From:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	nishimura@....nes.nec.co.jp,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
	"xemul@...nvz.org" <xemul@...nvz.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/4] memcg: set page->mapping NULL before uncharge

On Mon, 29 Sep 2008 19:22:40 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> This patch tries to make page->mapping to be NULL before
> mem_cgroup_uncharge_cache_page() is called.
> 
> "page->mapping == NULL" is a good check for "whether the page is still
> radix-tree or not".
> This patch also adds BUG_ON() to mem_cgroup_uncharge_cache_page();
> 
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> 
Looks good to me.

	Reviewed-by: Daisuke Nishimura <nishimura@....nes.nec.co.jp>

>  mm/filemap.c    |    2 +-
>  mm/memcontrol.c |    1 +
>  mm/migrate.c    |    9 +++++++--
>  3 files changed, 9 insertions(+), 3 deletions(-)
> 
> Index: mmotm-2.6.27-rc7+/mm/filemap.c
> ===================================================================
> --- mmotm-2.6.27-rc7+.orig/mm/filemap.c
> +++ mmotm-2.6.27-rc7+/mm/filemap.c
> @@ -116,12 +116,12 @@ void __remove_from_page_cache(struct pag
>  {
>  	struct address_space *mapping = page->mapping;
>  
> -	mem_cgroup_uncharge_cache_page(page);
>  	radix_tree_delete(&mapping->page_tree, page->index);
>  	page->mapping = NULL;
>  	mapping->nrpages--;
>  	__dec_zone_page_state(page, NR_FILE_PAGES);
>  	BUG_ON(page_mapped(page));
> +	mem_cgroup_uncharge_cache_page(page);
>  
>  	/*
>  	 * Some filesystems seem to re-dirty the page even after
> Index: mmotm-2.6.27-rc7+/mm/memcontrol.c
> ===================================================================
> --- mmotm-2.6.27-rc7+.orig/mm/memcontrol.c
> +++ mmotm-2.6.27-rc7+/mm/memcontrol.c
> @@ -734,6 +734,7 @@ void mem_cgroup_uncharge_page(struct pag
>  void mem_cgroup_uncharge_cache_page(struct page *page)
>  {
>  	VM_BUG_ON(page_mapped(page));
> +	VM_BUG_ON(page->mapping);
>  	__mem_cgroup_uncharge_common(page, MEM_CGROUP_CHARGE_TYPE_CACHE);
>  }
>  
> Index: mmotm-2.6.27-rc7+/mm/migrate.c
> ===================================================================
> --- mmotm-2.6.27-rc7+.orig/mm/migrate.c
> +++ mmotm-2.6.27-rc7+/mm/migrate.c
> @@ -330,8 +330,6 @@ static int migrate_page_move_mapping(str
>  	__inc_zone_page_state(newpage, NR_FILE_PAGES);
>  
>  	spin_unlock_irq(&mapping->tree_lock);
> -	if (!PageSwapCache(newpage))
> -		mem_cgroup_uncharge_cache_page(page);
>  
>  	return 0;
>  }
> @@ -341,6 +339,8 @@ static int migrate_page_move_mapping(str
>   */
>  static void migrate_page_copy(struct page *newpage, struct page *page)
>  {
> +	int anon;
> +
>  	copy_highpage(newpage, page);
>  
>  	if (PageError(page))
> @@ -378,8 +378,13 @@ static void migrate_page_copy(struct pag
>  #endif
>  	ClearPagePrivate(page);
>  	set_page_private(page, 0);
> +	/* page->mapping contains a flag for PageAnon() */
> +	anon = PageAnon(page);
>  	page->mapping = NULL;
>  
> +	if (!anon) /* This page was removed from radix-tree. */
> +		mem_cgroup_uncharge_cache_page(page);
> +
>  	/*
>  	 * If any waiters have accumulated on the new page then
>  	 * wake them up.
> 
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