Messages in this thread | | | Date | Fri, 7 Mar 2008 18:37:28 -0800 (PST) | From | Christoph Lameter <> | Subject | Re: [PATCH] [8/13] Enable the mask allocator for x86 |
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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?
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