linux-kernel - Re: [PATCH 2/2] mm: compaction: Minimise the time IRQs are disabled while isolating pages for migration

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Message-Id: <20110228145402.65e6f200.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Mon, 28 Feb 2011 14:54:02 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Andrea Arcangeli <aarcange@...hat.com>
Cc:	Mel Gorman <mel@....ul.ie>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arthur Marsh <arthur.marsh@...ernode.on.net>,
	Clemens Ladisch <cladisch@...glemail.com>,
	Linux-MM <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] mm: compaction: Minimise the time IRQs are disabled
 while isolating pages for migration

On Mon, 28 Feb 2011 06:48:18 +0100
Andrea Arcangeli <aarcange@...hat.com> wrote:

> On Mon, Feb 28, 2011 at 11:17:46AM +0900, KAMEZAWA Hiroyuki wrote:
> > BTW, I forget why we always take zone->lru_lock with IRQ disabled....
> 
> To decrease lock contention in SMP to deliver overall better
> performance (not sure how much it helps though). It was supposed to be
> hold for a very short time (PAGEVEC_SIZE) to avoid giving irq latency
> problems.
> 

memory hotplug uses MIGRATE_ISOLATED migrate types for scanning pfn range
without lru_lock. I wonder whether we can make use of it (the function
which memory hotplug may need rework for the compaction but  migrate_type can
be used, I think).

Hmm.
-Kame

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