Re: [PATCH] [8/13] Enable the mask allocator for x86

[Christoph Lameter]

On Fri, 7 Mar 2008, Andi Kleen wrote:

> - Disable old ZONE_DMA
> No fixed size ZONE_DMA now anymore. All existing users of __GFP_DMA rely 
> on the compat call to the maskable allocator in alloc/free_pages
> - Call maskable allocator initialization functions at boot
> - Add TRAD_DMA_MASK for the compat functions 
> - Remove dma_reserve call

This looks okay for the disabling part. But note that there are various 
uses of MAX_DMA_ADDRESS (sparsemem, bootmem allocator) that are currently 
suboptimal because they set a boundary at 16MB for allocation of 
potentially large operating system structures. That boundary continues to 
exist despite the removal of ZONE_DMA?

It would be better to remove ZONE_DMA32 instead and enlarge ZONE_DMA so 
that it can take over the role of ZONE_DMA. Set the boundary for 
MAX_DMA_ADDRESS to the boundary for ZONE_DMA32. Then the 
allocations for sparse and bootmem will be allocated above 4GB which 
leaves lots of the lower space available for 32 bit DMA capable devices.

Removal of ZONE_DMA32 would allow us to remove support for that zone from 
the kernel in general since x86_64 is the only user of that zone.

Trouble is likely that there are existing users that have the expectation 
of a 4GB boundary on ZONE_DMA32 and 16MB on ZONE_DMA (particularly old 
drivers). Could we not clean that up?


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/