linux-kernel - Re: [PATCH v6] page_alloc: allow migration of smaller hugepages during contig

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Message-ID: <aUVgoEiaXj94IBmW@gourry-fedora-PF4VCD3F>
Date: Fri, 19 Dec 2025 09:26:40 -0500
From: Gregory Price <gourry@...rry.net>
To: Wei Yang <richard.weiyang@...il.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org, kernel-team@...a.com,
	akpm@...ux-foundation.org, vbabka@...e.cz, surenb@...gle.com,
	mhocko@...e.com, jackmanb@...gle.com, hannes@...xchg.org,
	ziy@...dia.com, osalvador@...e.de, rientjes@...gle.com,
	david@...hat.com, joshua.hahnjy@...il.com, fvdl@...gle.com
Subject: Re: [PATCH v6] page_alloc: allow migration of smaller hugepages
 during contig_alloc

On Fri, Dec 19, 2025 at 12:08:00AM +0000, Wei Yang wrote:
> >+
> >+			page = compound_head(page);
> >+			order = compound_order(page);
> 
> The order is get from head page.
> 
> >+			if ((order >= MAX_FOLIO_ORDER) ||
> >+			    (nr_pages <= (1 << order)))
> >+				return false;
> >+
> >+			/* No need to check the pfns for this page */
> >+			i += (1 << order) - 1;
> 
> So this advance should based on "head page" instead of original page, right?
>

hm, I think the thought here was that since we're moving forward from
start of an aligned chunk, we'd never hit a non-head page - but this
may not be true.  

Will think about this for a bit.

~Gregory