linux-kernel - Re: [RFC PATCH] mm: page_alloc: Add kernel parameter to select maximum PCP batch scale number

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Message-ID: <3ea4b352-c679-45e8-8ab9-84ba074c3e88@tuxon.dev>
Date: Mon, 24 Mar 2025 16:25:35 +0200
From: Claudiu Beznea <claudiu.beznea@...on.dev>
To: corbet@....net, akpm@...ux-foundation.org, thuth@...hat.com,
 rostedt@...dmis.org, paulmck@...nel.org, xiongwei.song@...driver.com,
 ying.huang@...el.com
Cc: linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, geert+renesas@...der.be,
 wsa+renesas@...g-engineering.com,
 Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
Subject: Re: [RFC PATCH] mm: page_alloc: Add kernel parameter to select
 maximum PCP batch scale number

Hi,

On 26.11.2024 11:51, Claudiu wrote:
> From: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
> 
> Commit 52166607ecc9 ("mm: restrict the pcp batch scale factor to avoid
> too long latency") introduced default PCP (Per-CPU Pageset) batch size as
> a configuration flag. The configuration flag is CONFIG_PCP_BATCH_SCALE_MAX.
> 
> The ARM64 defconfig has CONFIG_PCP_BATCH_SCALE_MAX=5. This defconfig
> is used by a high range of SoCs.
> 
> The Renesas RZ/G3S SoC is a single CPU SoC, with L1$ (I-cache 32Kbytes,
> D-cache 32 Kbytes), L3$ (256 Kbytes), but no L2$. It is currently used in
> a configuration with 1 GiB RAM size. In this configuration, starting with
> commit 52166607ecc9 ("mm: restrict the pcp batch scale factor to avoid too
> long latency") the "bonnie++ -d /mnt -u root" benchmark takes ~14 minutes
> while previously it took ~10 minutes. The /mnt directory is mounted on SD
> card. Same behavior is reproduced on similar Renesas single core devices
> (e.g., Renesas RZ/G2UL).
> 
> Add a new kernel parameter to allow systems like Renesas RZ/G3S to
> continue have the same performance numbers with the default mainline
> ARM64 config. With pcp_batch_scale_max=5 (the default value) the bonnie++
> benchmark takes ~14 minutes while with pcp_batch_scale_max=0 it takes
> ~10 minutes.
> 
> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
> ---

Can you please let me know your input on this patch?

Thank you,
Claudiu