linux-kernel - Re: [PATCH v2 2/4] mm/huge_memory: replace can_split

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Message-ID: <6cce0756-cfe1-7b39-d81a-ba1b2cb32fb5@huawei.com>
Date: Tue, 25 Nov 2025 17:10:18 +0800
From: Miaohe Lin <linmiaohe@...wei.com>
To: Zi Yan <ziy@...dia.com>, "David Hildenbrand (Red Hat)" <david@...nel.org>
CC: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, 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>, 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 v2 2/4] mm/huge_memory: replace can_split_folio() with
 direct refcount calculation

On 2025/11/25 5:08, Zi Yan wrote:
> On 24 Nov 2025, at 14:22, David Hildenbrand (Red Hat) wrote:
> 

<snip>

> 
> BTW, this page flag reuse is really confusing. I see PG_checked is
> PG_owner_priv_1 too and __folio_migrate_mapping() uses folio_test_swapcache()
> to decide the number of i_pages entries. Wouldn’t that cause any issue?
> ext4 does not release_folio() for migration when PG_checked is set,
> ubifs clears PG_checked in release_folio(). I have not checked all other FS
> yet. Maybe later.

folio_test_swapbacked() is also checked in folio_test_swapcache:

static __always_inline bool folio_test_swapcache(struct folio *folio)
{
	return folio_test_swapbacked(folio) &&
			test_bit(PG_swapcache, folio_flags(folio, 0));
}

So IMHO the reuse of this page flag should work fine.

Thanks.
.