Re: [RFC PATCH 0/5] Support multiple pages allocation

[Zhang Yanfei]

ä 2013/7/10 8:31, Joonsoo Kim åé:
> On Thu, Jul 04, 2013 at 12:00:44PM +0200, Michal Hocko wrote:
>> On Thu 04-07-13 13:24:50, Joonsoo Kim wrote:
>>> On Thu, Jul 04, 2013 at 12:01:43AM +0800, Zhang Yanfei wrote:
>>>> On 07/03/2013 11:51 PM, Zhang Yanfei wrote:
>>>>> On 07/03/2013 11:28 PM, Michal Hocko wrote:
>>>>>> On Wed 03-07-13 17:34:15, Joonsoo Kim wrote:
>>>>>> [...]
>>>>>>> For one page allocation at once, this patchset makes allocator slower than
>>>>>>> before (-5%). 
>>>>>>
>>>>>> Slowing down the most used path is a no-go. Where does this slow down
>>>>>> come from?
>>>>>
>>>>> I guess, it might be: for one page allocation at once, comparing to the original
>>>>> code, this patch adds two parameters nr_pages and pages and will do extra checks
>>>>> for the parameter nr_pages in the allocation path.
>>>>>
>>>>
>>>> If so, adding a separate path for the multiple allocations seems better.
>>>
>>> Hello, all.
>>>
>>> I modify the code for optimizing one page allocation via likely macro.
>>> I attach a new one at the end of this mail.
>>>
>>> In this case, performance degradation for one page allocation at once is -2.5%.
>>> I guess, remained overhead comes from two added parameters.
>>> Is it unreasonable cost to support this new feature?
>>
>> Which benchmark you are using for this testing?
> 
> I use my own module which do allocation repeatedly.
> 
>>
>>> I think that readahead path is one of the most used path, so this penalty looks
>>> endurable. And after supporting this feature, we can find more use cases.
>>
>> What about page faults? I would oppose that page faults are _much_ more
>> frequent than read ahead so you really cannot slow them down.
> 
> You mean page faults for anon?
> Yes. I also think that it is much more frequent than read ahead.
> Before futher discussion, I will try to add a separate path
> for the multiple allocations.

Some days ago, I was thinking that this multiple allocation behaviour
may be useful for vmalloc allocations. So I think it is worth trying.

> 
> Thanks.
> 
>>
>> [...]
>> -- 
>> Michal Hocko
>> SUSE Labs
>>
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> 


-- 
Thanks.
Zhang Yanfei
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