linux-kernel - Re: [PATCH v3 1/4] mm/huge_memory: change folio_split_supported() to folio_check

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Message-ID: <46d5090c-a6c5-41de-91c4-dacac58e1f9b@kernel.org>
Date: Wed, 26 Nov 2025 10:54:55 +0100
From: "David Hildenbrand (Red Hat)" <david@...nel.org>
To: Zi Yan <ziy@...dia.com>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, Nico Pache <npache@...hat.com>,
 Ryan Roberts <ryan.roberts@....com>, Dev Jain <dev.jain@....com>,
 Barry Song <baohua@...nel.org>, Lance Yang <lance.yang@...ux.dev>,
 Miaohe Lin <linmiaohe@...wei.com>, Naoya Horiguchi
 <nao.horiguchi@...il.com>, Wei Yang <richard.weiyang@...il.com>,
 Balbir Singh <balbirs@...dia.com>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/4] mm/huge_memory: change folio_split_supported() to
 folio_check_splittable()

> -	/*
> -	 * Folios that just got truncated cannot get split. Signal to the
> -	 * caller that there was a race.
> -	 *
> -	 * TODO: this will also currently refuse shmem folios that are in the
> -	 * swapcache.
> -	 */
> -	if (!is_anon && !folio->mapping)
> -		return -EBUSY;
> -
>   	if (new_order >= old_order)
>   		return -EINVAL;
>   
> -	if (!folio_split_supported(folio, new_order, split_type, /* warn = */ true))
> -		return -EINVAL;
> -
> -	is_hzp = is_huge_zero_folio(folio);
> -	if (is_hzp) {
> -		pr_warn_ratelimited("Called split_huge_page for huge zero page\n");
> -		return -EBUSY;

As we are changing that case to a VM_WARN_ONCE(), is there some path 
where we might trigger that?

I'm wondering about the split_huge_pages_all() function in particular. I 
guess the "!folio_test_lru(folio)" would protect us?

Apart from that LGTM

Acked-by: David Hildenbrand (Red Hat) <david@...nel.org>

-- 
Cheers

David