lkml.org 
[lkml]   [2019]   [Aug]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] mm/mmap.c: refine data locality of find_vma_prev
On Wed 07-08-19 08:31:09, Wei Yang wrote:
> On Tue, Aug 06, 2019 at 11:29:52AM +0200, Vlastimil Babka wrote:
> >On 8/6/19 10:11 AM, Wei Yang wrote:
> >> When addr is out of the range of the whole rb_tree, pprev will points to
> >> the biggest node. find_vma_prev gets is by going through the right most
> >
> >s/biggest/last/ ? or right-most?
> >
> >> node of the tree.
> >>
> >> Since only the last node is the one it is looking for, it is not
> >> necessary to assign pprev to those middle stage nodes. By assigning
> >> pprev to the last node directly, it tries to improve the function
> >> locality a little.
> >
> >In the end, it will always write to the cacheline of pprev. The caller has most
> >likely have it on stack, so it's already hot, and there's no other CPU stealing
> >it. So I don't understand where the improved locality comes from. The compiler
> >can also optimize the patched code so the assembly is identical to the previous
> >code, or vice versa. Did you check for differences?
>
> Vlastimil
>
> Thanks for your comment.
>
> I believe you get a point. I may not use the word locality. This patch tries
> to reduce some unnecessary assignment of pprev.
>
> Original code would assign the value on each node during iteration, this is
> what I want to reduce.

Is there any measurable difference (on micro benchmarks or regular
workloads)?
--
Michal Hocko
SUSE Labs

\
 
 \ /
  Last update: 2019-08-07 09:52    [W:0.388 / U:0.128 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site