linux-kernel - Re: [PATCH 2/2] mm/memory-failure: improve large block size folio handling.

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Message-ID: <35d00740-0aa4-1d6d-87b8-ee973bcff792@huawei.com>
Date: Sat, 11 Oct 2025 17:07:38 +0800
From: Miaohe Lin <linmiaohe@...wei.com>
To: Matthew Wilcox <willy@...radead.org>, 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>,
	<linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-mm@...ck.org>, <david@...hat.com>, <jane.chu@...cle.com>,
	<kernel@...kajraghav.com>,
	<syzbot+e6367ea2fdab6ed46056@...kaller.appspotmail.com>,
	<syzkaller-bugs@...glegroups.com>
Subject: Re: [PATCH 2/2] mm/memory-failure: improve large block size folio
 handling.

On 2025/10/11 13:00, Matthew Wilcox wrote:
> On Sat, Oct 11, 2025 at 12:12:12PM +0800, Miaohe Lin wrote:
>>>  		folio_set_has_hwpoisoned(folio);
>>> -		if (try_to_split_thp_page(p, false) < 0) {
>>> +		/*
>>> +		 * If the folio cannot be split to order-0, kill the process,
>>> +		 * but split the folio anyway to minimize the amount of unusable
>>> +		 * pages.
>>> +		 */
>>> +		if (try_to_split_thp_page(p, new_order, false) || new_order) {
>>> +			/* get folio again in case the original one is split */
>>> +			folio = page_folio(p);
>>
>> If original folio A is split and the after-split new folio is B (A != B), will the
>> refcnt of folio A held above be missing? I.e. get_hwpoison_page() held the extra refcnt
>> of folio A, but we put the refcnt of folio B below. Is this a problem or am I miss
>> something?
> 
> That's how split works.

I read the code and see how split works. Thanks for point this out.

> 
> Zi Yan, the kernel-doc for folio_split() could use some attention.

That would be really helpful.

Thanks.
.

> First, it's not kernel-doc; the comment opens with /* instead of /**.
> Second, it says:
> 
>  * After split, folio is left locked for caller.
> 
> which isn't actually true, right?  The folio which contains
> @split_at will be locked.  Also, it will contain the additional
> reference which was taken on @folio by the caller.
> 
> .
>