On 01/09/2012 02:51 PM, Seth Jennings wrote:
> + area = &get_cpu_var(zs_map_area);
> + if (off + class->size <= PAGE_SIZE) {
> + /* this object is contained entirely within a page */
> + area->vm_addr = kmap_atomic(page);
> + } else {
> + /* this object spans two pages */
> + struct page *nextp;
> +
> + nextp = get_next_page(page);
> + BUG_ON(!nextp);
> +
> +
> + set_pte(area->vm_ptes[0], mk_pte(page, PAGE_KERNEL));
> + set_pte(area->vm_ptes[1], mk_pte(nextp, PAGE_KERNEL));
> +
> + /* We pre-allocated VM area so mapping can never fail */
> + area->vm_addr = area->vm->addr;
> + }
This bit appears to be trying to make kmap_atomic() variant that can map
two pages in to contigious virtual addresses. Instead of open-coding it
in a non-portable way like this, should we just make a new kmap_atomic()
variant that does this?
>From the way it's implemented, I _think_ you're guaranteed to get two
contiguous addresses if you do two adjacent kmap_atomics() on the same CPU:
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.
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