Re: [PATCH] mm/THP: Don't use HPAGE_SHIFT in transparent hugepage code

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

"Kirill A. Shutemov" <kirill@shutemov.name> writes:

> On Tue, May 07, 2013 at 02:22:32AM +0530, Aneesh Kumar K.V wrote:
>> From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
>> 
>> For architectures like powerpc that support multiple explicit hugepage
>> sizes, HPAGE_SHIFT indicate the default explicit hugepage shift. For
>> THP to work the hugepage size should be same as PMD_SIZE. So use
>> PMD_SHIFT directly. So move the define outside CONFIG_TRANSPARENT_HUGEPAGE
>> #ifdef because we want to use these defines in generic code with
>> if (pmd_trans_huge()) conditional.
>> 
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
>> ---
>>  include/linux/huge_mm.h | 10 +++-------
>>  1 file changed, 3 insertions(+), 7 deletions(-)
>> 
>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
>> index 528454c..cc276d2 100644
>> --- a/include/linux/huge_mm.h
>> +++ b/include/linux/huge_mm.h
>> @@ -58,12 +58,11 @@ extern pmd_t *page_check_address_pmd(struct page *page,
>>  
>>  #define HPAGE_PMD_ORDER (HPAGE_PMD_SHIFT-PAGE_SHIFT)
>>  #define HPAGE_PMD_NR (1<<HPAGE_PMD_ORDER)
>> +#define HPAGE_PMD_SHIFT PMD_SHIFT
>
> What about:
>
> #ifndef HPAGE_PMD_SHIFT
> #define HPAGE_PMD_SHIFT HPAGE_SHIFT
> #endif
>
> And define HPAGE_PMD_SHIFT in arch code if HPAGE_SHIFT is not
> suitable?


That would work for me provided the BUILD_BUG_ON is also taken care.
But is there a reason why we want to do that ? Will any value other
than PMD_SHIFT work ?

The below patch shows how we want to use these. To avoid those
BUILD_BUG_ON I ended up doing HUGE_PAGE_SIZE and HUGE_PAGE_MASK

https://lists.ozlabs.org/pipermail/linuxppc-dev/2013-April/105631.html

-aneesh

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