Re: [PATCH v4 11/13] mempolicy: apply page table walker on queue_pages_range()

Naoya Horiguchi
2014-07-01T21:52:19Z

On Tue, Jul 01, 2014 at 02:00:32PM -0700, Dave Hansen wrote:
> On 07/01/2014 10:07 AM, Naoya Horiguchi wrote:
> > queue_pages_range() does page table walking in its own way now, but there
> > is some code duplicate. This patch applies page table walker to reduce
> > lines of code.
> >
> > queue_pages_range() has to do some precheck to determine whether we really
> > walk over the vma or just skip it. Now we have test_walk() callback in
> > mm_walk for this purpose, so we can do this replacement cleanly.
> > queue_pages_test_walk() depends on not only the current vma but also the
> > previous one, so queue_pages->prev is introduced to remember it.
>
> Hi Naoya,
>
> The previous version of this patch caused a performance regression which
> was reported to you:
>
> http://marc.info/?l=linux-kernel&m=140375975525069&w=2
>
> Has that been dealt with in this version somehow?

I believe so, in previous version we called ->pte_entry() callback
for each pte entries, but in this version I stop doing this and
most of works are done in ->pmd_entry() callback, so the number
of function calls are reduced by about 1/512. And rather than that,
I just cleaned up queue_pages_* without major behavioral changes, so
the visible regression should be solved.

Thanks,
Naoya Horiguchi