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

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Message-ID: <Pine.LNX.4.64.0708141540140.364@schroedinger.engr.sgi.com>
Date:	Tue, 14 Aug 2007 15:41:53 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Andi Kleen <andi@...stfloor.org>
cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 4/9] Atomic reclaim: Save irq flags in vmscan.c

On Wed, 15 Aug 2007, Andi Kleen wrote:

> > Ok I have a vague idea on how this could but its likely that the 
> > changes make things worse rather than better. Additional reference to a 
> > new cacheline (per cpu but still), preempt disable. Lots of code at all
> > call sites. Interrupt enable/disable is quite efficient in recent 
> > processors.
> 
> The goal of this was not to be faster than interrupt disable,
> but to avoid the interrupt latency impact. This might be a problem
> when spending a lot of time inside the locks.

Both. They need to be fast too and not complicate the kernel too much. I 
have not seen a serious holdoff case. The biggest issue is still the 
zone->lru lock but interrupts are always disabled for that one already.


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