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

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Date:	Tue, 14 Aug 2007 15:20:28 -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:

> > > The interrupt handler shouldn't touch zone_flag. If it wants
> > > to it would need to be converted to a local_t and incremented/decremented
> > > (should be about the same cost at least on architectures with sane
> > > local_t implementation) 
> > 
> > That would mean we need to fork the code for reclaim?
> 
> Not with the local_t increment.

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.


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