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SubjectRe: [PATCH] hugetlb: call mmu notifiers on hugepage cow
On Fri, May 28, 2010 at 09:39:59AM -0700, Doug Doan wrote:
> On 05/28/2010 02:59 AM, Mel Gorman wrote:
>> On Thu, May 27, 2010 at 01:43:00PM -0700, Doug Doan wrote:
>>> From: Doug Doan<dougd@cray.com>
>>>
>>> When a copy-on-write occurs, we take one of two paths in handle_mm_fault:
>>> through handle_pte_fault for normal pages, or through hugetlb_fault for
>>> huge pages.
>>>
>>> In the normal page case, we eventually get to do_wp_page and call mmu
>>> notifiers via ptep_clear_flush_notify. There is no callout to the mmmu
>>> notifiers in the huge page case. This patch fixes that.
>>>
>>> Signed-off-by: Doug Doan<dougd@cray.com>
>>> ---
>>
>>> --- mm/hugetlb.c.orig 2010-05-27 13:07:58.569546314 -0700
>>> +++ mm/hugetlb.c 2010-05-26 14:41:06.449296524 -0700
>>> @@ -2345,11 +2345,17 @@ retry_avoidcopy:
>>> ptep = huge_pte_offset(mm, address& huge_page_mask(h));
>>> if (likely(pte_same(huge_ptep_get(ptep), pte))) {
>>> /* Break COW */
>>> + mmu_notifier_invalidate_range_start(mm,
>>> + address& huge_page_mask(h),
>>> + (address& huge_page_mask(h)) + huge_page_size(h));
>>
>> Should the address not already be aligned?
>
> I'm not seeing where the address was aligned before this point. The code
> just above aligns it:
>
> ptep = huge_pte_offset(mm, address& huge_page_mask(h));
> if (likely(pte_same(huge_ptep_get(ptep), pte))) {
> /* Break COW */
>

I'm sorry. You're right. I was looking at the copy_huge_page which was
not aligning the address. It should be but it's ultimately harmless as
the parameter is discarded.

Acked-by: Mel Gorman <mel@csn.ul.ie>

>> Otherwise, I don't see any problem.
>>
>>> huge_ptep_clear_flush(vma, address, ptep);
>>> set_huge_pte_at(mm, address, ptep,
>>> make_huge_pte(vma, new_page, 1));
>>> /* Make the old page be freed below */
>>> new_page = old_page;
>>> + mmu_notifier_invalidate_range_end(mm,
>>> + address& huge_page_mask(h),
>>> + (address& huge_page_mask(h)) + huge_page_size(h));
>>> }
>>> page_cache_release(new_page);
>>> page_cache_release(old_page);
>>
>>
>

--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab


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