Re: [PATCH v17 7/9] mm/page_reporting: Rotate reported pages to the tail of the list

Mel Gorman
2020-02-19T14:59:18Z

On Tue, Feb 11, 2020 at 02:47:08PM -0800, Alexander Duyck wrote:
> From: Alexander Duyck <alexander.h.duyck@linux.intel.com>
>
> Rather than walking over the same pages again and again to get to the pages
> that have yet to be reported we can save ourselves a significant amount of
> time by simply rotating the list so that when we have a full list of
> reported pages the head of the list is pointing to the next non-reported
> page. Doing this should save us some significant time when processing each
> free list.
>
> This doesn't gain us much in the standard case as all of the non-reported
> pages should be near the top of the list already. However in the case of
> page shuffling this results in a noticeable improvement. Below are the
> will-it-scale page_fault1 w/ THP numbers for 16 tasks with and without
> this patch.
>
> Without:
> tasks processes processes_idle threads threads_idle
> 16 8093776.25 0.17 5393242.00 38.20
>
> With:
> tasks processes processes_idle threads threads_idle
> 16 8283274.75 0.17 5594261.00 38.15
>
> Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>

Thanks for pulling this patch out and noting its impact. I think the
rotation is ok and if it turns out I missed something, it'll be
relatively easy to back out just the optimisation and leave the rest of
the feature intact.

Acked-by: Mel Gorman <mgorman@techsingularity.net>

--
Mel Gorman
SUSE Labs