linux-kernel - Re: [PATCH v3] mm/huge_memory: do not change split_huge

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Message-ID: <73c5557a-bc84-e1aa-d5d0-ad0ae57b55bb@huawei.com>
Date: Wed, 22 Oct 2025 15:01:48 +0800
From: Miaohe Lin <linmiaohe@...wei.com>
To: Zi Yan <ziy@...dia.com>
CC: <akpm@...ux-foundation.org>, <mcgrof@...nel.org>,
	<nao.horiguchi@...il.com>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	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>, "Matthew Wilcox
 (Oracle)" <willy@...radead.org>, Wei Yang <richard.weiyang@...il.com>,
	<linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-mm@...ck.org>, <stable@...r.kernel.org>, Pankaj Raghav
	<p.raghav@...sung.com>, <david@...hat.com>, <jane.chu@...cle.com>,
	<kernel@...kajraghav.com>,
	<syzbot+e6367ea2fdab6ed46056@...kaller.appspotmail.com>,
	<syzkaller-bugs@...glegroups.com>
Subject: Re: [PATCH v3] mm/huge_memory: do not change split_huge_page*()
 target order silently.

On 2025/10/17 9:36, Zi Yan wrote:
> Page cache folios from a file system that support large block size (LBS)
> can have minimal folio order greater than 0, thus a high order folio might
> not be able to be split down to order-0. Commit e220917fa507 ("mm: split a
> folio in minimum folio order chunks") bumps the target order of
> split_huge_page*() to the minimum allowed order when splitting a LBS folio.
> This causes confusion for some split_huge_page*() callers like memory
> failure handling code, since they expect after-split folios all have
> order-0 when split succeeds but in reality get min_order_for_split() order
> folios and give warnings.
> 
> Fix it by failing a split if the folio cannot be split to the target order.
> Rename try_folio_split() to try_folio_split_to_order() to reflect the added
> new_order parameter. Remove its unused list parameter.
> 
> Fixes: e220917fa507 ("mm: split a folio in minimum folio order chunks")
> [The test poisons LBS folios, which cannot be split to order-0 folios, and
> also tries to poison all memory. The non split LBS folios take more memory
> than the test anticipated, leading to OOM. The patch fixed the kernel
> warning and the test needs some change to avoid OOM.]
> Reported-by: syzbot+e6367ea2fdab6ed46056@...kaller.appspotmail.com
> Closes: https://lore.kernel.org/all/68d2c943.a70a0220.1b52b.02b3.GAE@google.com/
> Cc: stable@...r.kernel.org
> Signed-off-by: Zi Yan <ziy@...dia.com>
> Reviewed-by: Luis Chamberlain <mcgrof@...nel.org>
> Reviewed-by: Pankaj Raghav <p.raghav@...sung.com>
> Reviewed-by: Wei Yang <richard.weiyang@...il.com>

Thanks for your patch. LGTM.

Reviewed-by: Miaohe Lin <linmiaohe@...wei.com>

Thanks.
.