linux-kernel - Re: [PATCH v3] ARM64: Dynamically allocate cpumasks and increase supported CPUs to 512

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Date: Thu,  7 Mar 2024 19:07:07 +0000
From: Catalin Marinas <catalin.marinas@....com>
To: Mark Rutland <mark.rutland@....com>,
	"Christoph Lameter (Ampere)" <cl@...two.org>
Cc: Will Deacon <will@...nel.org>,
	Jonathan.Cameron@...wei.com,
	Matteo.Carlini@....com,
	akpm@...ux-foundation.org,
	anshuman.khandual@....com,
	Eric Mackay <eric.mackay@...cle.com>,
	dave.kleikamp@...cle.com,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	linux@...linux.org.uk,
	robin.murphy@....com,
	vanshikonda@...amperecomputing.com,
	yang@...amperecomputing.com,
	Valentin Schneider <vschneid@...hat.com>
Subject: Re: [PATCH v3] ARM64: Dynamically allocate cpumasks and increase supported CPUs to 512

On Wed, 06 Mar 2024 17:45:04 -0800, Christoph Lameter (Ampere) wrote:
> Currently defconfig selects NR_CPUS=256, but some vendors (e.g. Ampere
> Computing) are planning to ship systems with 512 CPUs. So that all CPUs on
> these systems can be used with defconfig, we'd like to bump NR_CPUS to 512.
> Therefore this patch increases the default NR_CPUS from 256 to 512.
> 
> As increasing NR_CPUS will increase the size of cpumasks, there's a fear that
> this might have a significant impact on stack usage due to code which places
> cpumasks on the stack. To mitigate that concern, we can select
> CPUMASK_OFFSTACK. As that doesn't seem to be a problem today with
> NR_CPUS=256, we only select this when NR_CPUS > 256.
> 
> [...]

Applied to arm64 (for-next/misc), thanks!

I dropped the config entry and comment, replaced it with a select as per
Mark's suggestion.

[1/1] ARM64: Dynamically allocate cpumasks and increase supported CPUs to 512
      https://git.kernel.org/arm64/c/0499a78369ad

-- 
Catalin