linux-kernel - Re: [PATCHv6 02/17] mm: Change the interface of prep_compound

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Message-ID: <aYR-YULI3lBtl9y_@thinkstation>
Date: Thu, 5 Feb 2026 11:35:50 +0000
From: Kiryl Shutsemau <kas@...nel.org>
To: "David Hildenbrand (arm)" <david@...nel.org>
Cc: 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>, 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 02/17] mm: Change the interface of prep_compound_tail()

On Wed, Feb 04, 2026 at 05:14:12PM +0100, David Hildenbrand (arm) wrote:
> On 2/2/26 16:56, Kiryl Shutsemau wrote:
> > Instead of passing down the head page and tail page index, pass the tail
> > and head pages directly, as well as the order of the compound page.
> > 
> > This is a preparation for changing how the head position is encoded in
> > the tail page.
> > 
> > Signed-off-by: Kiryl Shutsemau <kas@...nel.org>
> > Reviewed-by: Muchun Song <muchun.song@...ux.dev>
> > Reviewed-by: Zi Yan <ziy@...dia.com>
> > ---
> >   include/linux/page-flags.h |  4 +++-
> >   mm/hugetlb.c               |  8 +++++---
> >   mm/internal.h              | 12 ++++++------
> >   mm/mm_init.c               |  2 +-
> >   mm/page_alloc.c            |  2 +-
> >   5 files changed, 16 insertions(+), 12 deletions(-)
> > 
> > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> > index f7a0e4af0c73..8a3694369e15 100644
> > --- a/include/linux/page-flags.h
> > +++ b/include/linux/page-flags.h
> > @@ -865,7 +865,9 @@ static inline bool folio_test_large(const struct folio *folio)
> >   	return folio_test_head(folio);
> >   }
> > -static __always_inline void set_compound_head(struct page *page, struct page *head)
> > +static __always_inline void set_compound_head(struct page *page,
> > +					      const struct page *head,
> > +					      unsigned int order)
> 
> Two tab indents please on second+ parameter list whenever you touch code.

Do we have this coding style preference written down somewhere?

-tip tree wants the opposite. Documentation/process/maintainer-tip.rst:

	When splitting function declarations or function calls, then please align
	the first argument in the second line with the first argument in the first
	line::

I want the editor to do The Right Thing™ without my brain involvement.
Having different coding styles in different corners of the kernel makes
it hard.

> 
> >   {
> >   	WRITE_ONCE(page->compound_head, (unsigned long)head + 1);
> >   }
> > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> > index 6e855a32de3d..54ba7cd05a86 100644
> 
> 
> [...]
> 
> > diff --git a/mm/internal.h b/mm/internal.h
> > index d67e8bb75734..037ddcda25ff 100644
> > --- a/mm/internal.h
> > +++ b/mm/internal.h
> > @@ -879,13 +879,13 @@ static inline void prep_compound_head(struct page *page, unsigned int order)
> >   		INIT_LIST_HEAD(&folio->_deferred_list);
> >   }
> > -static inline void prep_compound_tail(struct page *head, int tail_idx)
> > +static inline void prep_compound_tail(struct page *tail,
> 
> Just wondering whether we should call this "struct page *page" for
> consistency with set_compound_head().
> 
> Or alternatively, call it also "tail" in set_compound_head().

I will take the alternative path :)

> 
> > +				      const struct page *head,
> > +				      unsigned int order)
> 
> Two tab indent, then this fits into two lines in total.
> 
> >   {
> > -	struct page *p = head + tail_idx;
> > -
> > -	p->mapping = TAIL_MAPPING;
> > -	set_compound_head(p, head);
> > -	set_page_private(p, 0);
> > +	tail->mapping = TAIL_MAPPING;
> > +	set_compound_head(tail, head, order);
> > +	set_page_private(tail, 0);
> >   }
> Only nits, in general LGTM
> 
> Acked-by: David Hildenbrand (arm) <david@...nel.org>

Thanks!

-- 
  Kiryl Shutsemau / Kirill A. Shutemov