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Date: Tue, 6 Feb 2024 23:17:58 +0000
From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: "Christoph Lameter (Ampere)" <cl@gentwo.org>
Cc: catalin.marinas@arm.com, Will Deacon <will@kernel.org>,
	Jonathan.Cameron@huawei.com, Matteo.Carlini@arm.com,
	Valentin.Schneider@arm.com, akpm@linux-foundation.org,
	anshuman.khandual@arm.com, Eric Mackay <eric.mackay@oracle.com>,
	dave.kleikamp@oracle.com, linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	robin.murphy@arm.com, vanshikonda@os.amperecomputing.com,
	yang@os.amperecomputing.com
Subject: Re: [PATCH REPOST v2] ARM64: Dynamically allocate cpumasks and
 increase supported CPUs to 512
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Sender: Russell King (Oracle) <linux@armlinux.org.uk>

On Tue, Feb 06, 2024 at 10:09:59AM -0800, Christoph Lameter (Ampere) wrote:
> Can we get this merged for 6.9? The patch has been around for awhile now.
> 
> 
> 
> Ampere Computing develops high end ARM processor that support an ever
> increasing number of processors. The default 256 processors are
> not enough for our newer products. The default is used by
> distros and therefore our customers cannot use distro kernels because
> the number of processors is not supported.
> 
> One of the objections against earlier patches to increase the limit
> was that the memory use becomes too high. There is a feature called
> CPUMASK_OFFSTACK that configures the cpumasks in the kernel to be
> dynamically allocated. This was used in the X86 architecture in the
> past to enable support for larger CPU configurations up to 8k cpus.
> 
> With that is becomes possible to dynamically size the allocation of
> the cpu bitmaps depending on the quantity of processors detected on
> bootup.
> 
> This patch enables that logic if more than 256 processors
> are configured and increases the default to 512 processors.
> 
> Further increases may be needed if ARM processor vendors start
> supporting more processors. Given the current inflationary trends
> in core counts from multiple processor manufacturers this may occur.
> 
> Tested-by: Eric Mackay <eric.mackay@oracle.com>

Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>

Thanks!

> Signed-off-by: Christoph Lameter (Ampere) <cl@linux.com>

-- 
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