linux-kernel - Re: [PATCH 0/3] Recalculate per-cpu page allocator batch and high limits after deferred meminit

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Date:   Fri, 18 Oct 2019 12:58:49 +0100
From:   Matt Fleming <matt@...eblueprint.co.uk>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, Linux-MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/3] Recalculate per-cpu page allocator batch and high
 limits after deferred meminit

On Fri, 18 Oct, at 11:56:03AM, Mel Gorman wrote:
> A private report stated that system CPU usage was excessive on an AMD
> EPYC 2 machine while building kernels with much longer build times than
> expected. The issue is partially explained by high zone lock contention
> due to the per-cpu page allocator batch and high limits being calculated
> incorrectly. This series addresses a large chunk of the problem. Patch 1
> is mostly cosmetic but prepares for patch 2 which is the real fix. Patch
> 3 is definiely cosmetic but was noticed while implementing the fix. Proper
> details are in the changelog for patch 2.
> 
>  include/linux/mm.h |  3 ---
>  mm/internal.h      |  3 +++
>  mm/page_alloc.c    | 33 ++++++++++++++++++++-------------
>  3 files changed, 23 insertions(+), 16 deletions(-)

Just to confirm, these patches don't fix the issue we're seeing on the
EPYC 2 machines, but they do return the batch sizes to sensible values.