From: "Zi Yan" <ziy@nvidia.com>
To: "David Hildenbrand (Arm)" <david@kernel.org>,
"Barry Song" <baohua@kernel.org>, "Ye Liu" <ye.liu@linux.dev>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
"Baolin Wang" <baolin.wang@linux.alibaba.com>,
"Liam R. Howlett" <liam@infradead.org>,
"Nico Pache" <nico.pache@linux.dev>,
"Ryan Roberts" <ryan.roberts@arm.com>,
"Dev Jain" <dev.jain@arm.com>,
"Lance Yang" <lance.yang@linux.dev>,
"Usama Arif" <usama.arif@linux.dev>,
"Kiryl Shutsemau" <kas@kernel.org>, <linux-mm@kvack.org>,
<linux-kernel@vger.kernel.org>, "Ye Liu" <liuye@kylinos.cn>
Subject: Re: [PATCH] mm/huge_memory: use READ_ONCE() when cloning folio flags during split
Date: Thu, 29 Oct 2026 15:19:09 -0400 [thread overview]
Message-ID: <DMHKCEKNMA64.3B6O5X5918GWI@nvidia.com> (raw)
In-Reply-To: <d44e0aef-ac50-4048-952b-50a0307a41cb@kernel.org>
On Thu Oct 29, 2026 at 10:54 AM EDT, David Hildenbrand (Arm) wrote:
> On 10/29/26 15:31, Zi Yan wrote:
>> On Thu Oct 29, 2026 at 6:47 AM EDT, David Hildenbrand (Arm) wrote:
>>> On 10/29/26 10:08, Barry Song wrote:
>>>>
>>>> I assume the race is harmless, but silencing KCSAN is still worthwhile.
>>
>> data_race() would work too.
>>
>>>
>>> Isn't there a way we could lose the PG_waiters flag?
>>
>> The PG_waiters on the original folio/the original head page is not lost,
>
> Ah, so it's not on arbitrary tail pages, just the old head.
>
>> but there is a chance PG_waiters is lost in the new head, because
>> prep_compound_page() uses __SetPageHead() and can ignore the atomic set
>> of PG_waiters.
>
> Fun.
> ...>
>> Solutions can be:
>>
>> 1. Use atomic SetPageHead() in prep_compound_page().
>
> That sounds like the right thing to do?
Yes, simpler, but the atomic op can be costly at compound page init
time. My plan is to add prep_compound_page_atomic() for
__split_folio_to_order() and the atomic version SetPageHead().
Fixes: c010d47f107f6 ("mm: thp: split huge page to any lower order pages").
Will send a patch soon.
--
Best Regards,
Yan, Zi
next prev parent reply other threads:[~2026-10-29 19:19 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-29 7:41 [PATCH] mm/huge_memory: use READ_ONCE() when cloning folio flags during split Ye Liu
2026-10-29 9:08 ` Barry Song
2026-10-29 10:47 ` David Hildenbrand (Arm)
2026-10-29 14:31 ` Zi Yan
2026-10-29 14:54 ` David Hildenbrand (Arm)
2026-10-29 19:19 ` Zi Yan [this message]
2026-10-29 19:24 ` David Hildenbrand (Arm)
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