mm: add framework for PCP high auto-tuning

The page allocation performance requirements of different workloads are
usually different.  So, we need to tune PCP (per-CPU pageset) high to
optimize the workload page allocation performance.  Now, we have a system
wide sysctl knob (percpu_pagelist_high_fraction) to tune PCP high by hand.
But, it's hard to find out the best value by hand.  And one global
configuration may not work best for the different workloads that run on
the same system.  One solution to these issues is to tune PCP high of each
CPU automatically.

This patch adds the framework for PCP high auto-tuning.  With it,
pcp->high of each CPU will be changed automatically by tuning algorithm at
runtime.  The minimal high (pcp->high_min) is the original PCP high value
calculated based on the low watermark pages.  While the maximal high
(pcp->high_max) is the PCP high value when percpu_pagelist_high_fraction
sysctl knob is set to MIN_PERCPU_PAGELIST_HIGH_FRACTION.  That is, the
maximal pcp->high that can be set via sysctl knob by hand.

It's possible that PCP high auto-tuning doesn't work well for some
workloads.  So, when PCP high is tuned by hand via the sysctl knob, the
auto-tuning will be disabled.  The PCP high set by hand will be used
instead.

This patch only adds the framework, so pcp->high will be set to
pcp->high_min (original default) always.  We will add actual auto-tuning
algorithm in the following patches in the series.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: "Huang, Ying" <[email protected]>
Acked-by: Mel Gorman <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Pavel Tatashin <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Arjan van de Ven <[email protected]>
Cc: Sudeep Holla <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

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