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

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Date:	Tue, 1 Mar 2011 00:07:12 +0100
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Minchan Kim <minchan.kim@...il.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 Tue, Mar 01, 2011 at 08:01:31AM +0900, Minchan Kim wrote:
> I am not sure it's good if we release the lock whenever lru->lock was contended
> unconditionally? There are many kinds of lru_lock operations(add to lru, 
> del from lru, isolation, reclaim, activation, deactivation and so on).

This is mostly to mirror cond_resched_lock (which actually uses
spin_needbreak but it's ok to have it also when preempt is off). I
doubt it makes a big difference but I tried to mirror
cond_resched_lock.

> Do we really need to release the lock whenever all such operations were contened?
> I think what we need is just spin_is_contended_irqcontext.
> Otherwise, please write down the comment for justifying for it.

What is spin_is_contended_irqcontext?

> This patch is for reducing for irq latency but do we have to check signal 
> in irq hold time?

I think it's good idea to check the signal in case the loop is very
long and this is run in direct compaction context.
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