linux-kernel - Re: [PATCH 1/4] vmstat: remove zone->lock from walk_zones_in

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Message-Id: <20100106093257.9E2B.A69D9226@jp.fujitsu.com>
Date:	Wed,  6 Jan 2010 09:33:44 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Mel Gorman <mel@....ul.ie>
Cc:	kosaki.motohiro@...fujitsu.com,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH 1/4] vmstat: remove zone->lock from walk_zones_in_node

> > Thanks lots comments. 
> > hmm.. I'd like to clarily your point. My point is memory-hotplug don't take zone lock,
> > then zone lock doesn't protect anything. so we have two option
> > 
> > 1) Add zone lock to memroy-hotplug
> > 2) Remove zone lock from zoneinfo
> > 
> > I thought (2) is sufficient. Do you mean you prefer to (1)? Or you prefer to ignore rarely event
> > (of cource, memory hotplug is rarely)?
> > 
> 
> I think (2) will make zoneinfo harder to use for examining all the counters
> properly as I explained above. I haven't looked at memory-hotplug in a
> while but IIRC, fields like present_pages should be protected by a lock on
> the pgdat and a seq lock on the zone. If this is not true at the moment,
> it is a problem.
> 
> For the free lists, memory hotplug should be taking the zone->lock properly as
> the final stage of onlining memory is to walk the sections being hot-added,
> init the memmap and then __free_page() each page individually - i.e. the
> normal free path.
> 
> So, if memory hotplug is not protected by proper locking, it's not intentional.

ok, I drop this patch. thanks.



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