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

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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>


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