Re: [PATCH 19/28] mm, page_alloc: Reduce cost of fair zone allocation policy retry

[Vlastimil Babka]

On 04/15/2016 11:07 AM, Mel Gorman wrote:
> The fair zone allocation policy is not without cost but it can be reduced
> slightly. This patch removes an unnecessary local variable, checks the
> likely conditions of the fair zone policy first, uses a bool instead of
> a flags check and falls through when a remote node is encountered instead
> of doing a full restart. The benefit is marginal but it's there
>
>                                             4.6.0-rc2                  4.6.0-rc2
>                                         decstat-v1r20              optfair-v1r20
> Min      alloc-odr0-1               377.00 (  0.00%)           380.00 ( -0.80%)
> Min      alloc-odr0-2               273.00 (  0.00%)           273.00 (  0.00%)
> Min      alloc-odr0-4               226.00 (  0.00%)           227.00 ( -0.44%)
> Min      alloc-odr0-8               196.00 (  0.00%)           196.00 (  0.00%)
> Min      alloc-odr0-16              183.00 (  0.00%)           183.00 (  0.00%)
> Min      alloc-odr0-32              175.00 (  0.00%)           173.00 (  1.14%)
> Min      alloc-odr0-64              172.00 (  0.00%)           169.00 (  1.74%)
> Min      alloc-odr0-128             170.00 (  0.00%)           169.00 (  0.59%)
> Min      alloc-odr0-256             183.00 (  0.00%)           180.00 (  1.64%)
> Min      alloc-odr0-512             191.00 (  0.00%)           190.00 (  0.52%)
> Min      alloc-odr0-1024            199.00 (  0.00%)           198.00 (  0.50%)
> Min      alloc-odr0-2048            204.00 (  0.00%)           204.00 (  0.00%)
> Min      alloc-odr0-4096            210.00 (  0.00%)           209.00 (  0.48%)
> Min      alloc-odr0-8192            213.00 (  0.00%)           213.00 (  0.00%)
> Min      alloc-odr0-16384           214.00 (  0.00%)           214.00 (  0.00%)
>
> The benefit is marginal at best but one of the most important benefits,
> avoiding a second search when falling back to another node is not triggered
> by this particular test so the benefit for some corner cases is understated.
>
> Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>

Acked-by: Vlastimil Babka <vbabka@xxxxxxx>