Re: ZERO_PAGE refcounting causes cache line bouncing

[Nick Piggin <nickpiggin@yahoo.com.au>]

Nick Piggin wrote:
> Nick Piggin wrote:
> 
>> Something like this roughly should get rid of ZERO_PAGE _count and 
>> _mapcount
>> manipulation for anonymous pages. (others still exist, XIP and 
>> /dev/zero, but
>> they should not be a large concern AFAIKS).
>>
>> I haven't booted this, but it is a quick forward port + some fixes and
>> simplifications.
>>
>>
>> ------------------------------------------------------------------------
>>
>> Index: linux-2.6/mm/memory.c
>> ===================================================================
>> --- linux-2.6.orig/mm/memory.c
>> +++ linux-2.6/mm/memory.c
>> @@ -665,7 +665,8 @@ static unsigned long zap_pte_range(struc
>>              ptent = ptep_get_and_clear_full(mm, addr, pte,
>>                              tlb->fullmm);
>>              tlb_remove_tlb_entry(tlb, pte, addr);
>> -            if (unlikely(!page))
>> +            if (unlikely(!page ||
>> +                (!vma->vm_file && page == ZERO_PAGE(addr))))
>>                  continue;
> 
> 
> Hmm, well I suppose it would be cleaner if this check used the one in
> handle_pte_fault instead of !vma->vm_file ie. (!vma->vm_ops ||
> !vma->vm_ops->nopage)

Bah, I also missed a reject for a similar hunk required in copy_one_pte.

I don't think there is anything more required after that, though... I
will actually test it tomorrow and send an updated patch with proper
changelog.

-- 
SUSE Labs, Novell Inc.
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