linux-kernel - Re: [PATCHv2 10/14] mm: Drop fake head checks

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Message-Id: <976A9938-0228-4230-92B2-7F6708E96199@linux.dev>
Date: Mon, 22 Dec 2025 13:56:25 +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 10/14] mm: Drop fake head checks



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

Thanks.