Re: [PATCH] improve __GFP_COLD/__GFP_ZERO interaction

["Kirill A. Shutemov" <kirill@shutemov.name>]

On Mon, Jun 02, 2014 at 04:27:52PM +0100, Jan Beulich wrote:
> >>> On 02.06.14 at 17:16, <kirill@shutemov.name> wrote:
> > On Mon, Jun 02, 2014 at 03:46:10PM +0100, Jan Beulich wrote:
> >> For cold page allocations using the normal clear_highpage() mechanism
> >> may be inefficient on certain architectures, namely due to needlessly
> >> replacing a good part of the data cache contents. Introduce an arch-
> >> overridable clear_cold_highpage() (using streaming non-temporal stores
> >> on x86, where an override gets implemented right away) to make use of
> >> in this specific case.
> >> 
> >> Leverage the impovement in the Xen balloon driver, eliminating the
> >> explicit scrub_page() function.
> > 
> > Any benchmark data?
> > 
> > I've tried non-temporal stores to clear huge pages, but it didn't helped
> > much. I believe it can vary between micro-architectures, but we need
> > numbers. I've played with Westmere that time.
> 
> It's not at all clear to me what to measure here - after all this isn't
> about improving the page clearing latency or throughput, but about
> avoiding to disturb other operations.

It would be nice to find a workload which benefits from not trashing cache
from page allocator.

-- 
 Kirill A. Shutemov

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