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SubjectRe: [PATCH V2 0/6] VA to numa node information
On Fri 14-09-18 12:01:18, Steven Sistare wrote:
> On 9/14/2018 1:56 AM, Michal Hocko wrote:
[...]
> > Why does this matter for something that is for analysis purposes.
> > Reading the file for the whole address space is far from a free
> > operation. Is the page walk optimization really essential for usability?
> > Moreover what prevents move_pages implementation to be clever for the
> > page walk itself? In other words why would we want to add a new API
> > rather than make the existing one faster for everybody.
>
> One could optimize move pages. If the caller passes a consecutive range
> of small pages, and the page walk sees that a VA is mapped by a huge page,
> then it can return the same numa node for each of the following VA's that fall
> into the huge page range. It would be faster than 55 nsec per small page, but
> hard to say how much faster, and the cost is still driven by the number of
> small pages.

This is exactly what I was arguing for. There is some room for
improvements for the existing interface. I yet have to hear the explicit
usecase which would required even better performance that cannot be
achieved by the existing API.

--
Michal Hocko
SUSE Labs

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