linux-kernel - Re: [patch v3] x86: allow ZONE

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Message-ID: <4DC09BBA.6040906@zytor.com>
Date:	Tue, 03 May 2011 17:20:10 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	David Rientjes <rientjes@...gle.com>
CC:	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch v3] x86: allow ZONE_DMA to be configurable

On 05/03/2011 05:00 PM, David Rientjes wrote:
> On Wed, 27 Apr 2011, David Rientjes wrote:
> 
>> ZONE_DMA is unnecessary for a large number of machines that do not
>> require addressing in the lower 16MB of memory because they do not use
>> devices with 16-bit address registers (plus one page byte register).
>>
>> This patch allows users to disable ZONE_DMA for x86 if they know they
>> will not be using such devices with their kernel.
>>
>> This prevents the VM from unnecessarily reserving a ratio of memory
>> (defaulting to 1/256th of system capacity) with lowmem_reserve_ratio
>> for such allocations when it will never be used.
>>
>> Signed-off-by: David Rientjes <rientjes@...gle.com>
> 
> Peter, is this ready for merge?


+ DMA memory allocation support allows devices with 16-bit address
+ registers to allocate memory within the first 16MB of address space.
+ Disable if no such devices will be used.

This is still not correct... this is for devices with less than a 32-bit
mask, not just for things that have 24-bit (not 16-bit!) DMA address
restrictions.

Please get this right.

Other than that, I don't have any technical objections.

	-hpa
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