linux-kernel - Re: [patch 6/8] mm: memcg: remove unneeded checks from uncharge

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Message-ID: <20111124090639.GD6843@cmpxchg.org>
Date:	Thu, 24 Nov 2011 10:06:39 +0100
From:	Johannes Weiner <hannes@...xchg.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.cz>,
	Balbir Singh <bsingharora@...il.com>, cgroups@...r.kernel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 6/8] mm: memcg: remove unneeded checks from
 uncharge_page()

On Thu, Nov 24, 2011 at 09:06:19AM +0900, KAMEZAWA Hiroyuki wrote:
> On Wed, 23 Nov 2011 16:42:29 +0100
> Johannes Weiner <hannes@...xchg.org> wrote:
> 
> > From: Johannes Weiner <jweiner@...hat.com>
> > 
> > mem_cgroup_uncharge_page() is only called on either freshly allocated
> > pages without page->mapping or on rmapped PageAnon() pages.  There is
> > no need to check for a page->mapping that is not an anon_vma.
> > 
> > Signed-off-by: Johannes Weiner <jweiner@...hat.com>
> 
> For making our assumption clearer to readers of codes,
> VM_BUG_ON(page->mapping && !PageAnon(page)) please.

Yep, delta patch below.

> Anyway,
> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

Thanks!

---
From: Johannes Weiner <jweiner@...hat.com>
Subject: mm: memcg: remove unneeded checks from uncharge_page() fix

Document page state assumptions and catch if they are violated in
uncharge_page().

Signed-off-by: Johannes Weiner <jweiner@...hat.com>
---
 mm/memcontrol.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 2f1fdc4..872dae1 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2992,6 +2992,7 @@ void mem_cgroup_uncharge_page(struct page *page)
 	/* early check. */
 	if (page_mapped(page))
 		return;
+	VM_BUG_ON(page->mapping && !PageAnon(page));
 	__mem_cgroup_uncharge_common(page, MEM_CGROUP_CHARGE_TYPE_MAPPED);
 }
 
-- 
1.7.6.4

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