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SubjectRe: [mm PATCH v3 1/6] mm: Use mm_zero_struct_page from SPARC on all 64b architectures
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On 10/17/2018 12:30 AM, Mike Rapoport wrote:
> On Tue, Oct 16, 2018 at 03:01:11PM -0400, Pavel Tatashin wrote:
>>
>>
>> On 10/15/18 4:26 PM, Alexander Duyck wrote:
>>> This change makes it so that we use the same approach that was already in
>>> use on Sparc on all the archtectures that support a 64b long.
>>>
>>> This is mostly motivated by the fact that 8 to 10 store/move instructions
>>> are likely always going to be faster than having to call into a function
>>> that is not specialized for handling page init.
>>>
>>> An added advantage to doing it this way is that the compiler can get away
>>> with combining writes in the __init_single_page call. As a result the
>>> memset call will be reduced to only about 4 write operations, or at least
>>> that is what I am seeing with GCC 6.2 as the flags, LRU poitners, and
>>> count/mapcount seem to be cancelling out at least 4 of the 8 assignments on
>>> my system.
>>>
>>> One change I had to make to the function was to reduce the minimum page
>>> size to 56 to support some powerpc64 configurations.
>>>
>>> Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
>>
>>
>> I have tested on Broadcom's Stingray cpu with 48G RAM:
>> __init_single_page() takes 19.30ns / 64-byte struct page
>> Wit the change it takes 17.33ns / 64-byte struct page
>
> I gave it a run on an OpenPower (S812LC 8348-21C) with Power8 processor and
> with 128G of RAM. My results for 64-byte struct page were:
>
> before: 4.6788ns
> after: 4.5882ns
>
> My two cents :)

Thanks. I will add this and Pavel's data to the patch description.

- Alex

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