linux-kernel - Re: [PATCH v7] page_alloc: allow migration of smaller hugepages during contig

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <9c807ff8-b4ad-43d5-8034-ec7fcd0fe5d6@kernel.org>
Date: Tue, 6 Jan 2026 19:46:25 +0100
From: "David Hildenbrand (Red Hat)" <david@...nel.org>
To: Gregory Price <gourry@...rry.net>, linux-mm@...ck.org
Cc: 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,
 richard.weiyang@...il.com
Subject: Re: [PATCH v7] page_alloc: allow migration of smaller hugepages
 during contig_alloc

> -			return false;
> +		/*
> +		 * Only consider ranges containing hugepages if those pages are
> +		 * smaller than the requested contiguous region.  e.g.:
> +		 *     Move 2MB pages to free up a 1GB range.
> +		 *     Don't move 1GB pages to free up a 2MB range.
> +		 *
> +		 * This makes contiguous allocation more reliable if multiple
> +		 * hugepage sizes are used without causing needless movement.
> +		 */
> +		if (PageHuge(page)) {
> +			unsigned int order;
> +
> +			if (!IS_ENABLED(CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION))
> +				return false;
> +
> +			if (skip_hugetlb) {
> +				*skipped_hugetlb = true;
> +				return false;
> +			}
> +
> +			page = compound_head(page);
> +			order = compound_order(page);
> +			if ((order >= MAX_FOLIO_ORDER) ||
> +			    (nr_pages <= (1 << order)))
> +				return false;
> +
> +			/*
> +			 * Reaching this point means we've encounted a huge page
> +			 * smaller than nr_pages, skip all pfn's for that page.
> +			 *
> +			 * We can't get here from a tail-PageHuge, as it implies
> +			 * we started a scan in the middle of a hugepage larger
> +			 * than nr_pages - which the prior check filters for.
> +			 */
> +			i += (1 << order) - 1;

Assuming page != compound_head(page), you'd be skipping too much.

You'd only have to skip as many pages as pages are left in this compound 
page.

I think we have similar code elsewhere: see has_unmovable_pages().

Apart from that LGTM.

-- 
Cheers

David