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

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Message-ID: <20210524092530.GE30378@techsingularity.net>
Date:   Mon, 24 May 2021 10:25:30 +0100
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Linux-MM <linux-mm@...ck.org>,
        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 Fri, May 21, 2021 at 03:57:20PM -0700, Dave Hansen wrote:
> 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>

Thanks, I updated the changelog and hopefully it is better.

-- 
Mel Gorman
SUSE Labs