linux-kernel - Re: [PATCH -V3 6/9] mm: add framework for PCP high auto-tuning

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Date:   Thu, 19 Oct 2023 13:16:40 +0100
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Huang Ying <ying.huang@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Arjan Van De Ven <arjan@...ux.intel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        David Hildenbrand <david@...hat.com>,
        Johannes Weiner <jweiner@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Michal Hocko <mhocko@...e.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Matthew Wilcox <willy@...radead.org>,
        Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH -V3 6/9] mm: add framework for PCP high auto-tuning

On Mon, Oct 16, 2023 at 01:29:59PM +0800, Huang Ying wrote:
> 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.
> 
> Signed-off-by: "Huang, Ying" <ying.huang@...el.com>

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

-- 
Mel Gorman
SUSE Labs