linux-kernel - Re: [PATCHv4 05/14] mm: Rework compound_head() for power-of-2 sizeof(struct page)

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Message-ID: <aXIKBhHd7IbaJkXg@thinkstation>
Date: Thu, 22 Jan 2026 11:29:43 +0000
From: Kiryl Shutsemau <kas@...nel.org>
To: Zi Yan <ziy@...dia.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, 
	Muchun Song <muchun.song@...ux.dev>, 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>, 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: [PATCHv4 05/14] mm: Rework compound_head() for power-of-2
 sizeof(struct page)

On Wed, Jan 21, 2026 at 12:12:13PM -0500, Zi Yan wrote:
> > @@ -1244,8 +1244,8 @@ void snapshot_page(struct page_snapshot *ps, const struct page *page)
> >  again:
> >  	memset(&ps->folio_snapshot, 0, sizeof(struct folio));
> >  	memcpy(&ps->page_snapshot, page, sizeof(*page));
> > -	head = ps->page_snapshot.compound_info;
> > -	if ((head & 1) == 0) {
> > +	info = ps->page_snapshot.compound_info;
> > +	if ((info & 1) == 0) {
> 
> This could be “if (!(info & 1))” like _compound_head(), right?

Right. But I don't see why it has to change.


-- 
  Kiryl Shutsemau / Kirill A. Shutemov