On 02/06/2012 09:26 AM, Seth Jennings wrote:
> On 01/26/2012 01:12 PM, Dave Hansen wrote:
>> void *kmap_atomic_prot(struct page *page, pgprot_t prot)
>> {
>> ...
>> type = kmap_atomic_idx_push();
>> idx = type + KM_TYPE_NR*smp_processor_id();
>> vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx);
>>
>> I think if you do a get_cpu()/put_cpu() or just a preempt_disable()
>> across the operations you'll be guaranteed to get two contiguous addresses.
>
> I'm not quite following here. kmap_atomic() only does this for highmem pages.
> For normal pages (all pages for 64-bit), it doesn't do any mapping at all. It
> just returns the virtual address of the page since it is in the kernel's address
> space.
>
> For this design, the pages _must_ be mapped, even if the pages are directly
> reachable in the address space, because they must be virtually contiguous.
I guess you could use vmap() for that. It's just going to be slower
than kmap_atomic(). I'm really not sure it's worth all the trouble to
avoid order-1 allocations, though.
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