linux-kernel - Re: [PATCHv2 11/14] hugetlb: Remove VMEMMAP_SYNCHRONIZE

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Message-Id: <48BA4DA6-DE9D-4F07-B347-19D2F68B357A@linux.dev>
Date: Mon, 22 Dec 2025 14:00:09 +0800
From: Muchun Song <muchun.song@...ux.dev>
To: Kiryl Shutsemau <kas@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 David Hildenbrand <david@...nel.org>,
 Matthew Wilcox <willy@...radead.org>,
 Usama Arif <usamaarif642@...il.com>,
 Frank van der Linden <fvdl@...gle.com>,
 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>,
 kernel-team@...a.com,
 linux-mm@...ck.org,
 linux-kernel@...r.kernel.org,
 linux-doc@...r.kernel.org
Subject: Re: [PATCHv2 11/14] hugetlb: Remove VMEMMAP_SYNCHRONIZE_RCU



> On Dec 18, 2025, at 23:09, Kiryl Shutsemau <kas@...nel.org> 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>

Thanks.