linux-kernel - Re: [PATCH Resend] mm: Refine __{pgd,p4d,pud,pmd,pte}_alloc_one

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Message-Id: <0fbcde0d-4fed-4aa6-b0bf-c4400b9b1cf5@app.fastmail.com>
Date: Fri, 07 Nov 2025 12:21:38 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Huacai Chen" <chenhuacai@...ngson.cn>,
 "Huacai Chen" <chenhuacai@...nel.org>,
 "Andrew Morton" <akpm@...ux-foundation.org>
Cc: "Vishal Moola" <vishal.moola@...il.com>,
 "Kevin Brodsky" <kevin.brodsky@....com>, "Jan Kara" <jack@...e.cz>,
 linux-mm@...ck.org, Linux-Arch <linux-arch@...r.kernel.org>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH Resend] mm: Refine __{pgd,p4d,pud,pmd,pte}_alloc_one_*() about
 HIGHMEM

On Fri, Nov 7, 2025, at 10:59, Huacai Chen wrote:
> __{pgd,p4d,pud,pmd,pte}_alloc_one_*() always allocate pages with GFP
> flag GFP_PGTABLE_KERNEL/GFP_PGTABLE_USER. These two macros are defined
> as follows:
>
>  #define GFP_PGTABLE_KERNEL	(GFP_KERNEL | __GFP_ZERO)
>  #define GFP_PGTABLE_USER	(GFP_PGTABLE_KERNEL | __GFP_ACCOUNT)
>
> There is no __GFP_HIGHMEM in them, so we needn't to clear __GFP_HIGHMEM
> explicitly.
>
> Signed-off-by: Huacai Chen <chenhuacai@...ngson.cn>
> ---
> Resend because the lines begin with # was eaten by git.

Thanks for your patch, this is an area I've also started
looking at, with the intention to reduce the references
to __GFO_HIGHMEM to the minimum we need for supporting the
remaining platforms that need to use highmem somewhere.

I'm not sure what the reason is for your patch, I assume
this is meant purely as a cleanup, correct? Are you looking
at a wider set of related cleanups, or did you just notice
this one instance?

Note that for the moment, the 32-bit arm __pte_alloc_one() function
still passes __GFP_HIGHMEM when CONFIG_HIGHPTE is set, though
I would like to remove that code path. Unless we remove
that at the same time, this should probably be explained in your
patch description.

      Arnd