linux-kernel - Re: [PATCH v2 5/9] mm/huge_memory: mark PMD mappings of the huge zero folio special

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Message-ID: <20250728084955.uzobxwoqalcuhk72@master>
Date: Mon, 28 Jul 2025 08:49:55 +0000
From: Wei Yang <richard.weiyang@...il.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	xen-devel@...ts.xenproject.org, linux-fsdevel@...r.kernel.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>,
	Matthew Wilcox <willy@...radead.org>, Jan Kara <jack@...e.cz>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...e.com>, Zi Yan <ziy@...dia.com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	Nico Pache <npache@...hat.com>, Ryan Roberts <ryan.roberts@....com>,
	Dev Jain <dev.jain@....com>, Barry Song <baohua@...nel.org>,
	Jann Horn <jannh@...gle.com>, Pedro Falcato <pfalcato@...e.de>,
	Hugh Dickins <hughd@...gle.com>, Oscar Salvador <osalvador@...e.de>,
	Lance Yang <lance.yang@...ux.dev>
Subject: Re: [PATCH v2 5/9] mm/huge_memory: mark PMD mappings of the huge
 zero folio special

On Thu, Jul 17, 2025 at 01:52:08PM +0200, David Hildenbrand wrote:
>The huge zero folio is refcounted (+mapcounted -- is that a word?)
>differently than "normal" folios, similarly (but different) to the ordinary
>shared zeropage.
>
>For this reason, we special-case these pages in
>vm_normal_page*/vm_normal_folio*, and only allow selected callers to
>still use them (e.g., GUP can still take a reference on them).
>
>vm_normal_page_pmd() already filters out the huge zero folio. However,
>so far we are not marking it as special like we do with the ordinary
>shared zeropage. Let's mark it as special, so we can further refactor
>vm_normal_page_pmd() and vm_normal_page().
>
>While at it, update the doc regarding the shared zero folios.
>
>Reviewed-by: Oscar Salvador <osalvador@...e.de>
>Signed-off-by: David Hildenbrand <david@...hat.com>

Reviewed-by: Wei Yang <richard.weiyang@...il.com>

-- 
Wei Yang
Help you, Help me