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

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Message-ID: <28c262360912282005x68315a62l7ffde637febc7646@mail.gmail.com>
Date:	Tue, 29 Dec 2009 13:05:37 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	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>,
	Mel Gorman <mel@....ul.ie>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH 1/4] vmstat: remove zone->lock from walk_zones_in_node

On Mon, Dec 28, 2009 at 4:47 PM, KOSAKI Motohiro
<kosaki.motohiro@...fujitsu.com> wrote:
> The zone->lock is one of performance critical locks. Then, it shouldn't
> be hold for long time. Currently, we have four walk_zones_in_node()
> usage and almost use-case don't need to hold zone->lock.

I agree.

We can use walk_zone_in_node freely to show the information related to zone.

- frag_show_print : the number of free pages per order.
- pagetypeinfo_showfree_print : the number of free page per migration type
- pagetypeinfo_showblockcount_print : the number of pages in zone per
migration type
- zoneinfo_show_print : many info about zone.

Do we want to show exact value? No.
If we want it, it's not enough zone->lock only.
After all, All of things would be transient value.

>
> Thus, this patch move locking responsibility from walk_zones_in_node
> to its sub function. Also this patch kill unnecessary zone->lock taking.
>
> Cc: Mel Gorman <mel@....ul.ie>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Reviewed-by: Minchan Kim <minchan.kim@...il.com>

-- 
Kind regards,
Minchan Kim
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