linux-kernel - Re: [PATCH][-mm] Fix setup_per_zone_pages

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Message-Id: <20070907111650.0e0bf01f.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 7 Sep 2007 11:16:50 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Mel Gorman <mel@....ul.ie>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH][-mm] Fix setup_per_zone_pages_min() lock.

On Thu, 06 Sep 2007 14:53:01 +0100
Mel Gorman <mel@....ul.ie> wrote:

> Does it really matter as they routinely do not take zone->lru_lock
> either? pages_min, pages_low and pages_high are currently examined on a
> regular basis by zone_watermark_ok() without any locks held in the page
> allocator and page reclaim path. Glancing through this, it would appear
> that the code in question has the same level of locking protection with
> zone->lru_lock or zone->lock.
> 
At the first look, I thought this should be lock-less. But I noticed that
memory hotplug(See add_memory()) calls  setup_per_zone_pages_min().
Then, logically, there are 2 interfaces which calls  setup_per_zone_pages_min();
So, we need some kind of lock. 

And setup_zone_migrate_reserve() is also called in this function.
This does more than change value. So I thought zone->lock is good here.

> Is memory hotadd specifically taking the lru_lock somewhere? I can only
> think of the seqlock at the moment.
> 
memory hotplug doesn't take lru_lock.


Thanks,
-Kame

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