linux-kernel - Re: [PATCH] memcg: lock-free clear page writeback (Was Re: [PATCH 04/10] memcg: disable local interrupts in lock_page

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Date:	Thu, 7 Oct 2010 18:05:29 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Minchan Kim <minchan.kim@...il.com>,
	Greg Thelen <gthelen@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	containers@...ts.osdl.org, Andrea Righi <arighi@...eler.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>
Subject: Re: [PATCH] memcg: lock-free clear page writeback  (Was Re: [PATCH
 04/10] memcg: disable local interrupts in lock_page_cgroup()

On Thu, 7 Oct 2010 15:24:22 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:

> Greg, I think clear_page_writeback() will not require _any_ locks with this patch.
> But set_page_writeback() requires it...
> (Maybe adding a special function for clear_page_writeback() is better rather than
>  adding some complex to switch() in update_page_stat())
> 

I'm testing a code like this.
==
       /* pc->mem_cgroup is unstable ? */
        if (unlikely(mem_cgroup_stealed(mem))) {
                /* take a lock against to access pc->mem_cgroup */
                if (!in_interrupt()) {
                        lock_page_cgroup(pc);
                        need_unlock = true;
                        mem = pc->mem_cgroup;
                        if (!mem || !PageCgroupUsed(pc))
                                goto out;
                } else if (idx == MEMCG_NR_FILE_WRITEBACK && (val < 0)) {
                        /* This is allowed */
                } else
                        BUG();
        }
==
Thanks,
-Kame

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