linux-kernel - Re: [RFC 4/9] Atomic reclaim: Save irq flags in vmscan.c

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Message-ID: <20070814214430.GD23308@one.firstfloor.org>
Date:	Tue, 14 Aug 2007 23:44:30 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Christoph Lameter <clameter@....com>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC 4/9] Atomic reclaim: Save irq flags in vmscan.c

On Tue, Aug 14, 2007 at 02:37:27PM -0700, Christoph Lameter wrote:
> On Tue, 14 Aug 2007, Andi Kleen wrote:
> 
> > > We already have such a flag in the zone structure
> > 
> > Zone structure is not strictly CPU local so it's broader
> > than needed. But it might work.
> 
> We could convert this into a per cpu array?

Perhaps. That would make it more expensive to read for
its current users though. 

> But that still creates lots of overhead each time we take the lru lock!

A lot of overhead in what way? Setting a flag in a cache hot
per CPU data variable shouldn't be more than a few cycles.

-Andi
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