linux-kernel - Re: [PATCHv6 12/17] mm: Drop fake head checks

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Message-ID: <f80f6ea8-2988-461b-ad6d-c1b23408c45f@suse.cz>
Date: Tue, 10 Feb 2026 17:18:44 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Kiryl Shutsemau <kas@...nel.org>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Muchun Song <muchun.song@...ux.dev>, David Hildenbrand <david@...hat.com>,
 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>,
 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 12/17] mm: Drop fake head checks

On 2/2/26 16:56, Kiryl Shutsemau wrote:
> With fake head pages eliminated in the previous commit, remove the
> supporting infrastructure:
> 
>   - page_fixed_fake_head(): no longer needed to detect fake heads;
>   - page_is_fake_head(): no longer needed;
>   - page_count_writable(): no longer needed for RCU protection;
>   - RCU read_lock in page_ref_add_unless(): no longer needed;
> 
> This substantially simplifies compound_head() and page_ref_add_unless(),
> removing both branches and RCU overhead from these hot paths.
> 
> Signed-off-by: Kiryl Shutsemau <kas@...nel.org>
> Reviewed-by: Muchun Song <muchun.song@...ux.dev>

Reviewed-by: Vlastimil Babka <vbabka@...e.cz>