Re: [PATCH 20/28] mm, page_alloc: Shortcut watermark checks for order-0 pages

[Vlastimil Babka]

On 04/15/2016 11:07 AM, Mel Gorman wrote:
> Watermarks have to be checked on every allocation including the number of
> pages being allocated and whether reserves can be accessed. The reserves
> only matter if memory is limited and the free_pages adjustment only applies
> to high-order pages. This patch adds a shortcut for order-0 pages that avoids
> numerous calculations if there is plenty of free memory yielding the following
> performance difference in a page allocator microbenchmark;
>
>                                             4.6.0-rc2                  4.6.0-rc2
>                                         optfair-v1r20             fastmark-v1r20
> Min      alloc-odr0-1               380.00 (  0.00%)           364.00 (  4.21%)
> Min      alloc-odr0-2               273.00 (  0.00%)           262.00 (  4.03%)
> Min      alloc-odr0-4               227.00 (  0.00%)           214.00 (  5.73%)
> Min      alloc-odr0-8               196.00 (  0.00%)           186.00 (  5.10%)
> Min      alloc-odr0-16              183.00 (  0.00%)           173.00 (  5.46%)
> Min      alloc-odr0-32              173.00 (  0.00%)           165.00 (  4.62%)
> Min      alloc-odr0-64              169.00 (  0.00%)           161.00 (  4.73%)
> Min      alloc-odr0-128             169.00 (  0.00%)           159.00 (  5.92%)
> Min      alloc-odr0-256             180.00 (  0.00%)           168.00 (  6.67%)
> Min      alloc-odr0-512             190.00 (  0.00%)           180.00 (  5.26%)
> Min      alloc-odr0-1024            198.00 (  0.00%)           190.00 (  4.04%)
> Min      alloc-odr0-2048            204.00 (  0.00%)           196.00 (  3.92%)
> Min      alloc-odr0-4096            209.00 (  0.00%)           202.00 (  3.35%)
> Min      alloc-odr0-8192            213.00 (  0.00%)           206.00 (  3.29%)
> Min      alloc-odr0-16384           214.00 (  0.00%)           206.00 (  3.74%)
>
> Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>

Acked-by: Vlastimil Babka <vbabka@xxxxxxx>