Re: [patch v3] x86: allow ZONE_DMA to be configurable

["H. Peter Anvin" <hpa@zytor.com>]

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@google.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