On Thu, 2008-05-29 at 22:20 +1000, npiggin@xxxxxxx wrote:
> +int get_user_pages_fast(unsigned long start, int nr_pages, int write, struct page **pages)
> +{
> + struct mm_struct *mm = current->mm;
> + unsigned long end = start + (nr_pages << PAGE_SHIFT);
> + unsigned long addr = start;
> + unsigned long next;
> + pgd_t *pgdp;
> + int nr = 0;
> +
> + if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
> + start, nr_pages*PAGE_SIZE)))
> + goto slow_irqon;
> +
> + /*
> + * XXX: batch / limit 'nr', to avoid large irq off latency
> + * needs some instrumenting to determine the common sizes used by
> + * important workloads (eg. DB2), and whether limiting the batch size
> + * will decrease performance.
> + *
> + * It seems like we're in the clear for the moment. Direct-IO is
> + * the main guy that batches up lots of get_user_pages, and even
> + * they are limited to 64-at-a-time which is not so many.
> + */
> + /*
> + * This doesn't prevent pagetable teardown, but does prevent
> + * the pagetables and pages from being freed on x86.
> + *
> + * So long as we atomically load page table pointers versus teardown
> + * (which we do on x86, with the above PAE exception), we can follow the
> + * address down to the the page and take a ref on it.
> + */
> + local_irq_disable();
> + pgdp = pgd_offset(mm, addr);
> + do {
> + pgd_t pgd = *pgdp;
> +
> + next = pgd_addr_end(addr, end);
> + if (pgd_none(pgd))
> + goto slow;
> + if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
> + goto slow;
> + } while (pgdp++, addr = next, addr != end);
> + local_irq_enable();
> +
> + VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT);
> + return nr;
> +
> + {
> + int i, ret;
> +
> +slow:
> + local_irq_enable();
> +slow_irqon:
> + /* Try to get the remaining pages with get_user_pages */
> + start += nr << PAGE_SHIFT;
> + pgaes += nr;
Typo: s/pgaes/pages/
> +
> + down_read(&mm->mmap_sem);
> + ret = get_user_pages(current, mm, start,
> + (end - start) >> PAGE_SHIFT, write, 0, pages, NULL);
> + up_read(&mm->mmap_sem);
> +
> + /* Have to be a bit careful with return values */
> + if (nr > 0) {
> + if (ret < 0)
> + ret = nr;
> + else
> + ret += nr;
> + }
> +
> + return ret;
> + }
> +}
--
David Kleikamp
IBM Linux Technology Center
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