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    SubjectRe: [PATCH 1/5] staging: zsmalloc: zsmalloc memory allocation library
    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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