linux-kernel - Re: [PATCH v7 6/6] arm64: mm: Optimize linear_map_split_to

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Message-ID: <aLnFpndf-XikPPFf@arm.com>
Date: Thu, 4 Sep 2025 18:00:22 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Ryan Roberts <ryan.roberts@....com>
Cc: Will Deacon <will@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Hildenbrand <david@...hat.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Yang Shi <yang@...amperecomputing.com>,
	Ard Biesheuvel <ardb@...nel.org>, Dev Jain <dev.jain@....com>,
	scott@...amperecomputing.com, cl@...two.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH v7 6/6] arm64: mm: Optimize linear_map_split_to_ptes()

On Fri, Aug 29, 2025 at 12:52:47PM +0100, Ryan Roberts wrote:
> When splitting kernel leaf mappings, either via
> split_kernel_leaf_mapping_locked() or linear_map_split_to_ptes(),
> previously a leaf mapping was always split to the next size down. e.g.
> pud -> contpmd -> pmd -> contpte -> pte. But for
> linear_map_split_to_ptes() we can avoid the contpmd and contpte states
> because we know we want to split all the way down to ptes.
> 
> This avoids visiting all the ptes in a table if it was created by
> splitting a pmd, which is noticible on systems with a lot of memory.
> 
> Signed-off-by: Ryan Roberts <ryan.roberts@....com>

Reviewed-by: Catalin Marinas <catalin.marinas@....com>