linux-kernel - Re: [PATCHv6 13/17] hugetlb: Remove VMEMMAP_SYNCHRONIZE

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Message-ID: <ad1a6ccd-d542-420f-b862-b41b7a29054b@kernel.org>
Date: Fri, 6 Feb 2026 10:42:24 +0100
From: "David Hildenbrand (Arm)" <david@...nel.org>
To: Kiryl Shutsemau <kas@...nel.org>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Muchun Song <muchun.song@...ux.dev>, Matthew Wilcox <willy@...radead.org>,
 Usama Arif <usamaarif642@...il.com>, Frank van der Linden <fvdl@...gle.com>
Cc: Oscar Salvador <osalvador@...e.de>, Mike Rapoport <rppt@...nel.org>,
 Vlastimil Babka <vbabka@...e.cz>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Zi Yan <ziy@...dia.com>,
 Baoquan He <bhe@...hat.com>, Michal Hocko <mhocko@...e.com>,
 Johannes Weiner <hannes@...xchg.org>, Jonathan Corbet <corbet@....net>,
 Huacai Chen <chenhuacai@...nel.org>, WANG Xuerui <kernel@...0n.name>,
 Palmer Dabbelt <palmer@...belt.com>, Paul Walmsley
 <paul.walmsley@...ive.com>, Albert Ou <aou@...s.berkeley.edu>,
 Alexandre Ghiti <alex@...ti.fr>, kernel-team@...a.com, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
 loongarch@...ts.linux.dev, linux-riscv@...ts.infradead.org
Subject: Re: [PATCHv6 13/17] hugetlb: Remove VMEMMAP_SYNCHRONIZE_RCU

On 2/2/26 16:56, Kiryl Shutsemau wrote:
> The VMEMMAP_SYNCHRONIZE_RCU flag triggered synchronize_rcu() calls to
> prevent a race between HVO remapping and page_ref_add_unless(). The
> race could occur when a speculative PFN walker tried to modify the
> refcount on a struct page that was in the process of being remapped
> to a fake head.
> 
> With fake heads eliminated, page_ref_add_unless() no longer needs RCU
> protection.
> 
> Remove the flag and synchronize_rcu() calls.
> 
> Signed-off-by: Kiryl Shutsemau <kas@...nel.org>
> Reviewed-by: Muchun Song <muchun.song@...ux.dev>
> ---

Reviewed-by: David Hildenbrand (Arm) <david@...nel.org>

-- 
Cheers,

David