Received-SPF: pass (google.com: domain of linux-kernel+bounces-64700-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
From: Zi Yan <ziy@nvidia.com>
To: Luis Chamberlain <mcgrof@kernel.org>
Cc: "\"Pankaj Raghav (Samsung)\"" <kernel@pankajraghav.com>,
 linux-mm@kvack.org, "\"Matthew Wilcox (Oracle)\"" <willy@infradead.org>,
 David Hildenbrand <david@redhat.com>, Yang Shi <shy828301@gmail.com>,
 Yu Zhao <yuzhao@google.com>,
 "\"Kirill A . Shutemov\"" <kirill.shutemov@linux.intel.com>,
 Ryan Roberts <ryan.roberts@arm.com>,
 =?utf-8?q?=22Michal_Koutn=C3=BD=22?= <mkoutny@suse.com>,
 Roman Gushchin <roman.gushchin@linux.dev>,
 "\"Zach O'Keefe\"" <zokeefe@google.com>, Hugh Dickins <hughd@google.com>,
 Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org,
 cgroups@vger.kernel.org, linux-fsdevel@vger.kernel.org,
 linux-kselftest@vger.kernel.org
Subject: Re: [PATCH v4 5/7] mm: thp: split huge page to any lower order pages
 (except order-1).
Date: Tue, 13 Feb 2024 21:56:45 -0500
Message-ID: <5CF2076E-E56F-4E79-AD95-F58111A623C7@nvidia.com>
In-Reply-To: <0A9F291F-E6B3-48C0-A2B5-3C893F02AE1D@nvidia.com>
References: <20240213215520.1048625-1-zi.yan@sent.com>
 <20240213215520.1048625-6-zi.yan@sent.com>
 <Zcvns2HCB61cwvgE@bombadil.infradead.org>
 <698B47BD-5E5E-4B8F-A998-8692A4918A5D@nvidia.com>
 <0A9F291F-E6B3-48C0-A2B5-3C893F02AE1D@nvidia.com>
Content-Type: multipart/signed;
 boundary="=_MailMate_AEEA94DD-FD34-48DA-AA55-B24C5F506FC5_=";
 micalg=pgp-sha512; protocol="application/pgp-signature"
Precedence: bulk
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0:
	=?us-ascii?Q?KBHfPTQb3jcBYS5DRI3vY311D9/ULCxE6avPIvN5VyJgDqu/eAbPSDqF1DMY?=
 =?us-ascii?Q?PHK5TnJctyFtQh3cQe3HCaZC9lF7lvdVaKRtT7qAamUUTb7qIHfLW7dWTMR3?=
 =?us-ascii?Q?lNTJ4kOZU5PfwjcOfTyYhtf5ySdS0QgrnBXoDxIHAYEno+tNKIcrlagtyu0o?=
 =?us-ascii?Q?AmiNFF7NwuTRRjMIx6DwYMA/IJeKPKchtfBi7Hb080SSRMXQBWOCQZmhl1Z4?=
 =?us-ascii?Q?wtWmdGDFy5fX1RQPQzt5ZLCMJ3uVecV6UbNOybZV62e+4m4auXX8wXA0w/N4?=
 =?us-ascii?Q?JHl+TIWZ0hLgJ1qfpVUGUmYv4nyf6gSUwThNrC2aR+WIunL8Mvbl3CeQF5W0?=
 =?us-ascii?Q?iIyoc6G4on2tDKfb7EIkROTB3GXzGeNQh/G+P5foXha3CnxOOdjdZlpciBPX?=
 =?us-ascii?Q?xgzJDEm0cuMUF9WeOxf5CF9eZP+g4CE4oyORPLUWhUosAbNIGHoerNeo7Gvq?=
 =?us-ascii?Q?ETHACMy0dUmca+SWOy0HhAmh5+3kKpzyT7CLSFw8xSfuig4kqpKEjdyRBRC1?=
 =?us-ascii?Q?rpKdbiimmrO9T7CBMth5RbnQv6EgSExC4v5eAi8S994SWf4oB5lx3xPkc0y0?=
 =?us-ascii?Q?b5eoqRtfIRY1BRX0FoQKuVo2tq5bKLV1VnD2e7WxLuTNH3zuB2DdDNNdpCuE?=
 =?us-ascii?Q?d3fChX/7PxPp5SYLnM54GOC91uFlQeS71wApqPca+xCPYVu2yytsbqKGibTo?=
 =?us-ascii?Q?uIiwVeAuirbaM8lMKsJCVEjT73uaYXA7P4teGUEabDy7Hh4NDTvboqNFFvNa?=
 =?us-ascii?Q?OOOSUeZtUWG1V1tnxkdXabm4tCNPwKy2jksADIUXyMDUMT4lVG6+7t7cPOMg?=
 =?us-ascii?Q?zlZfYzI/R1gk88wag0BPAEJvucoNc0/G4S52kTPt5UxK00uhe8AIy+YY3TuK?=
 =?us-ascii?Q?gLaCcTzyvZyF8a9Zof/0fyPL0gxmsCtOyeiZM4KBbabYTrzQjscCGRzBAmkM?=
 =?us-ascii?Q?y6qUYekx7mez0uakMrc1iSdxQcaGW78Hg55DtSQq3B94HMuwMPyIoLEn3KqY?=
 =?us-ascii?Q?cR/lEI37xzlTRoufZG7iLWqt22MXJcPr+tChK7gT907kvg7vQaxrgdCaHcaD?=
 =?us-ascii?Q?ZB056QJVQgdpLGiDffNytzbhyRBu17f66AVY96N6k9A47l8UGlCYfcrzHBkz?=
 =?us-ascii?Q?6vgb41FN/dYwgA8u8uzoZ4oZnDGnArVX/PGmSw/QqZe2rrF4umkMepFcstEq?=
 =?us-ascii?Q?3isTjDLTrG0g7BoU9vGFbZf3qFfoxBeIrvB9XryGr8MPDa+t0Ye5JtWHxJf2?=
 =?us-ascii?Q?R+An/jCVSl5rO0/jBWudyzoA65lwHBMNlhSNt+hxQiWpBTWdRozvHli6Tuoi?=
 =?us-ascii?Q?0x1bBIavy5Vvdflx6PUmy7T4YqpzbVW0AZAtOnUPqYeRn/25bH3vtGys+isn?=
 =?us-ascii?Q?zqZ/uBn7OR9OBDbv58S4K+TBNQ4w+FjsqJcDU8oOLZoRSquVGif/pp0W96sP?=
 =?us-ascii?Q?YCMsAcKbx2oxfMTIAF5DmB/Q3xMH2jlICgYjqjnMc6Y851H6QcTVdu++7o9a?=
 =?us-ascii?Q?1NgRcrF/94Cp+26kSxt/FAptvsXQ5c6kd67TAAoBixq8p+dxYXw4Gy06PAk0?=
 =?us-ascii?Q?So/pU8g+nTinmOaOOLo=3D?=
X-OriginatorOrg: Nvidia.com
X-MS-Exchange-CrossTenant-Network-Message-Id: 5386b68e-7915-4753-3dd1-08dc2d0895e8
X-MS-Exchange-CrossTenant-AuthSource: DS7PR12MB5744.namprd12.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 14 Feb 2024 02:56:47.9015
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: 6k3ob/sqmiyvuK8ShnwUOLOwatuoEWldxO3CrFJ+4k86O85On+qlfYXI3J4aMBLd
X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY8PR12MB7315

--=_MailMate_AEEA94DD-FD34-48DA-AA55-B24C5F506FC5_=
Content-Type: text/plain
Content-Transfer-Encoding: quoted-printable

On 13 Feb 2024, at 17:19, Zi Yan wrote:

> On 13 Feb 2024, at 17:15, Zi Yan wrote:
>
>> On 13 Feb 2024, at 17:05, Luis Chamberlain wrote:
>>
>>> On Tue, Feb 13, 2024 at 04:55:18PM -0500, Zi Yan wrote:
>>>> From: Zi Yan <ziy@nvidia.com>
>>>> Order-1 folio is not supported because _deferred_list, which is used=
 by
>>>> partially mapped folios, is stored in subpage 2 and an order-1 folio=
 only
>>>> has subpage 0 and 1.
>>>
>>> The LBS patches has the patch from Matthew which enables and allowed =
us
>>> to successfully test order 1. So this restriction could be dropped if=

>>> that gets merged.
>>
>> OK. But it only applies to file-backed folios IIUC. Anonymous folios s=
till
>> cannot be split to order-1.
>
> Something like this would lift the restriction:

Actually this, since folio_prep_large_rmappable() is changed by that patc=
h:

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 0564b007cbd1..05eeeafaa9dc 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2852,7 +2852,7 @@ static void __split_huge_page_tail(struct folio *fo=
lio, int tail,
        clear_compound_head(page_tail);
        if (new_order) {
                prep_compound_page(page_tail, new_order);
-               folio_prep_large_rmappable(page_folio(page_tail));
+               new_folio =3D folio_prep_large_rmappable(new_folio);
        }

        /* Finally unfreeze refcount. Additional reference from page cach=
e. */
@@ -3045,9 +3045,9 @@ int split_huge_page_to_list_to_order(struct page *p=
age, struct list_head *list,
        VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
        VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);

-       /* Cannot split THP to order-1 (no order-1 THPs) */
-       if (new_order =3D=3D 1) {
-               VM_WARN_ONCE(1, "Cannot split to order-1 folio");
+       /* Cannot split anonymous folios to order-1 (no order-1 anon foli=
os) */
+       if (new_order =3D=3D 1 && folio_test_anon(folio)) {
+               VM_WARN_ONCE(1, "Cannot split to order-1 anonymous folio"=
);
                return -EINVAL;
        }

--
Best Regards,
Yan, Zi

--=_MailMate_AEEA94DD-FD34-48DA-AA55-B24C5F506FC5_=
Content-Description: OpenPGP digital signature
Content-Disposition: attachment; filename=signature.asc
Content-Type: application/pgp-signature; name=signature.asc

-----BEGIN PGP SIGNATURE-----
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=RqS/
-----END PGP SIGNATURE-----

--=_MailMate_AEEA94DD-FD34-48DA-AA55-B24C5F506FC5_=--