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Date: Thu, 14 May 2009 22:20:45 +0530
From: Balbir Singh <balbir@linux.vnet.ibm.com>
Subject: mem_cgroup_lru_del_before_commit_swapcache() seems broken
Message-ID: <20090514165045.GA4451@balbir.in.ibm.com>
Reply-To: balbir@linux.vnet.ibm.com
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Sender: owner-linux-mm@kvack.org
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, "nishimura@mxp.nes.nec.co.jp" <nishimura@mxp.nes.nec.co.jp>
Cc: Andrew Morton <akpm@linux-foundation.org>, "linux-mm@kvack.org" <linux-mm@kvack.org>, "lizf@cn.fujitsu.com" <lizf@cn.fujitsu.com>, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
List-ID: <linux-mm.kvack.org>

Hi, Kame,

mem_cgroup_lru_del_before_commit_swapcache() seems to be broken, here
is why


static void mem_cgroup_lru_del_before_commit_swapcache(struct page
*page)
{
        unsigned long flags;
        struct zone *zone = page_zone(page);
        struct page_cgroup *pc = lookup_page_cgroup(page);

        spin_lock_irqsave(&zone->lru_lock, flags);
        /*
         * Forget old LRU when this page_cgroup is *not* used. This
         * Used bit
         * is guarded by lock_page() because the page is SwapCache.
         */
        if (!PageCgroupUsed(pc))
                mem_cgroup_del_lru_list(page, page_lru(page));

...
...
void mem_cgroup_del_lru_list(struct page *page, enum lru_list lru)
{
        struct page_cgroup *pc;
        struct mem_cgroup *mem;
        struct mem_cgroup_per_zone *mz;

        if (mem_cgroup_disabled())
                return;
        pc = lookup_page_cgroup(page);
        /* can happen while we handle swapcache. */
        if (!PageCgroupUsed(pc))
                return;


In mem_cgroup_lru_del_before_commit_swapcache() we say
        if (!PageCgroupused(pc))
                mem_cgroup_del_lru_list()

in mem_cgroup_del_lru_list() we say
        if (!PageCgroupUsed(pc))
                return;

So why call mem_cgroup_del_lru_list() at all? Am I missing something.

-- 
	Balbir

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