linux-kernel - Re: [PATCH 6/6] mm/page_alloc: Introduce vm.percpu_pagelist_high

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Message-ID: <ab7cbd43-7952-ca23-0a5c-379dfcfb14ba@intel.com>
Date:   Fri, 21 May 2021 15:57:20 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Mel Gorman <mgorman@...hsingularity.net>,
        Linux-MM <linux-mm@...ck.org>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Matthew Wilcox <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...nel.org>,
        Nicholas Piggin <npiggin@...il.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 6/6] mm/page_alloc: Introduce
 vm.percpu_pagelist_high_fraction

On 5/21/21 3:28 AM, Mel Gorman wrote:
> This introduces a new sysctl vm.percpu_pagelist_high_fraction. It is
> similar to the old vm.percpu_pagelist_fraction except it only adjusts
> pcp->high to potentially reduce zone->lock contention while preserving
> allocation latency when PCP lists have to be refilled.

Look at me...  Five patches later and I already forgot what the old one
did and why it stinks.  I wonder if you might do a wee bit of compare
and contrast.  Something like:

	The old vm.percpu_pagelist_fraction increased both the batch and
	high limits for the per-cpu page allocator.  Its worst feature
	was that it led to absurdly large batch sizes that incurred
	nasty worst-case allocation latency.

	This new sysctl in comparison...

Anyway, the approach looks sound to me.  The batch size isn't important
now, especially given the auto-scaling in patch 4.

Acked-by: Dave Hansen <dave.hansen@...ux.intel.com>