linux-kernel - Re: [PATCH RFC 10/14] mm/memory: factor out common code from vm_normal_page

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Message-ID: <aFu5Bn2APcr2sf7k@localhost.localdomain>
Date: Wed, 25 Jun 2025 10:53:26 +0200
From: Oscar Salvador <osalvador@...e.de>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, nvdimm@...ts.linux.dev,
	Andrew Morton <akpm@...ux-foundation.org>,
	Juergen Gross <jgross@...e.com>,
	Stefano Stabellini <sstabellini@...nel.org>,
	Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Alistair Popple <apopple@...dia.com>,
	Matthew Wilcox <willy@...radead.org>, Jan Kara <jack@...e.cz>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>, Zi Yan <ziy@...dia.com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Nico Pache <npache@...hat.com>, Ryan Roberts <ryan.roberts@....com>,
	Dev Jain <dev.jain@....com>, Barry Song <baohua@...nel.org>,
	Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...e.com>, Jann Horn <jannh@...gle.com>,
	Pedro Falcato <pfalcato@...e.de>
Subject: Re: [PATCH RFC 10/14] mm/memory: factor out common code from
 vm_normal_page_*()

On Tue, Jun 17, 2025 at 05:43:41PM +0200, David Hildenbrand wrote:
> Let's reduce the code duplication and factor out the non-pte/pmd related
> magic into vm_normal_page_pfn().
> 
> To keep it simpler, check the pfn against both zero folios. We could
> optimize this, but as it's only for the !CONFIG_ARCH_HAS_PTE_SPECIAL
> case, it's not a compelling micro-optimization.
> 
> With CONFIG_ARCH_HAS_PTE_SPECIAL we don't have to check anything else,
> really.
> 
> It's a good question if we can even hit the !CONFIG_ARCH_HAS_PTE_SPECIAL
> scenario in the PMD case in practice: but doesn't really matter, as
> it's now all unified in vm_normal_page_pfn().
> 
> While at it, add a check that pmd_special() is really only set where we
> would expect it.
> 
> No functional change intended.
> 
> Signed-off-by: David Hildenbrand <david@...hat.com>

Reviewed-by: Oscar Salvador <osalvador@...e.de>

Comment below

>  struct folio *vm_normal_folio(struct vm_area_struct *vma, unsigned long addr,
> @@ -650,35 +661,12 @@ struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr,
>  {
>  	unsigned long pfn = pmd_pfn(pmd);
>  
> -	/* Currently it's only used for huge pfnmaps */

Although the check kind of spells it out, we could leave this one and also add
that huge_zero_pfn, to make it more explicit.
 

-- 
Oscar Salvador
SUSE Labs