linux-kernel - Re: [PATCH 1/6] mm/page_alloc: Delete vm.percpu_pagelist

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Message-ID: <7b821c1f-ecc2-5e09-3c06-a63945d697ea@suse.cz>
Date:   Wed, 26 May 2021 19:41:05 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Mel Gorman <mgorman@...hsingularity.net>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Hillf Danton <hdanton@...a.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Michal Hocko <mhocko@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH 1/6] mm/page_alloc: Delete vm.percpu_pagelist_fraction

On 5/25/21 10:01 AM, Mel Gorman wrote:
> The vm.percpu_pagelist_fraction is used to increase the batch and high
> limits for the per-cpu page allocator (PCP). The intent behind the sysctl
> is to reduce zone lock acquisition when allocating/freeing pages but it has
> a problem. While it can decrease contention, it can also increase latency
> on the allocation side due to unreasonably large batch sizes. This leads
> to games where an administrator adjusts percpu_pagelist_fraction on the
> fly to work around contention and allocation latency problems.
> 
> This series aims to alleviate the problems with zone lock contention while
> avoiding the allocation-side latency problems. For the purposes of review,
> it's easier to remove this sysctl now and reintroduce a similar sysctl
> later in the series that deals only with pcp->high.
> 
> Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
> Acked-by: Dave Hansen <dave.hansen@...ux.intel.com>

Acked-by: Vlastimil Babka <vbabka@...e.cz>