Re: [RFC PATCH 0/5] Support multiple pages allocation
From: Michal Hocko
Date: Thu Jul 04 2013 - 06:00:57 EST
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 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.
[...]
--
Michal Hocko
SUSE Labs
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