Re: [patch 1/1] alloc_pages(): permit get_zeroed_page(GFP_ATOMIC) from interrupt context

On Mon, 27 Aug 2007 14:20:57 -0700 (PDT)
Christoph Lameter [off-list ref] wrote:

kmap_atomic() does:

void *kmap_atomic_prot(struct page *page, enum km_type type, pgprot_t prot)
{
        enum fixed_addresses idx;
        unsigned long vaddr;

        /* even !CONFIG_PREEMPT needs this, for in_atomic in do_page_fault */
        pagefault_disable();

        idx = type + KM_TYPE_NR*smp_processor_id();
        BUG_ON(!pte_none(*(kmap_pte-idx)));

        if (!PageHighMem(page))
                return page_address(page);

        vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx);
        set_pte(kmap_pte-idx, mk_pte(page, prot));
        arch_flush_lazy_mmu_mode();

        return (void*) vaddr;
}

Move the check for highmem to the beginning of the function? Why 
should kmap_atomic fail for a non highmem page?

For test coverage, mainly.  If someone is testing highmem-enabled code on
a 512MB machine, we want them to get told about any highmem-handling bugs,
even though they don't have highmem.

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