linux-kernel - Re: A question about ZONE

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Message-ID: <alpine.DEB.2.00.1010131351520.15185@chino.kir.corp.google.com>
Date:	Wed, 13 Oct 2010 13:53:42 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Casey Dahlin <cdahlin@...hat.com>
cc:	linux-kernel@...r.kernel.org
Subject: Re: A question about ZONE_DMA

On Wed, 13 Oct 2010, Casey Dahlin wrote:

> Hi all,
> 
> So if I understand correctly, ZONE_DMA exists to separate and preserve the
> chunk of memory to which older ISA cards are capable of doing DMA. The question
> that arises for me is:
> 
> 1) Why do /all/ 32-bit boxes have a ZONE_DMA when surely only a tiny and
> shrinking number of them have a need for it?
> 

If you don't need it, disable CONFIG_ZONE_DMA, which is useful to prevent 
oom conditions when lowmem_reserve_ratio reserves memory in that zone that 
you'll never need to save.

If you do disable that option, you may also want to look at disabling 
CONFIG_GENERIC_ISA_DMA and CONFIG_ISA_DMA_API which you need to hack a 
little to get to compile.  I'll send a patch to fix that.
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