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

[Joonsoo Kim]

On Wed, Jul 10, 2013 at 09:20:27AM +0800, Zhang Yanfei wrote:
> 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.

Yeh! I think so!

Thanks.

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