linux-kernel - Re: [PATCHv4 09/14] mm/hugetlb: Remove fake head pages

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Message-ID: <aXjPf_fIWX74YVWD@thinkstation>
Date: Tue, 27 Jan 2026 14:51:43 +0000
From: Kiryl Shutsemau <kas@...nel.org>
To: Muchun Song <muchun.song@...ux.dev>
Cc: 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, 
	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>
Subject: Re: [PATCHv4 09/14] mm/hugetlb: Remove fake head pages

On Thu, Jan 22, 2026 at 03:00:03PM +0800, Muchun Song wrote:
> > +	if (pfn)
> > +		return pfn_to_page(pfn);
> > +
> > +	tail = alloc_pages_node(node, GFP_KERNEL | __GFP_ZERO, 0);
> > +	if (!tail)
> > +		return NULL;
> > +
> > +	p = page_to_virt(tail);
> > +	for (int i = 0; i < PAGE_SIZE / sizeof(struct page); i++)
> > +		prep_compound_tail(p + i, NULL, order);
> > +
> > +	spin_lock(&hugetlb_lock);
> 
> hugetlb_lock is considered a contended lock, better not to abuse it.
> cmpxchg() is enought in this case.

We hit the lock once per node (excluding races). Its contribution to the
lock contention is negligible. spin_lock() is easier to follow. I will
keep it.

Ack for the rest of your comments.


-- 
  Kiryl Shutsemau / Kirill A. Shutemov