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Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 1/2] mm/huge_memory: move unrelated code out of __split_unmapped_folio() Date: Mon, 14 Jul 2025 11:33:20 -0400 X-Mailer: MailMate (2.0r6272) Message-ID: In-Reply-To: References: <20250711182355.3592618-1-ziy@nvidia.com> <20250711182355.3592618-2-ziy@nvidia.com> Content-Type: text/plain Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: BL1PR13CA0257.namprd13.prod.outlook.com (2603:10b6:208:2ba::22) To DS7PR12MB9473.namprd12.prod.outlook.com (2603:10b6:8:252::5) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS7PR12MB9473:EE_|DM4PR12MB6184:EE_ X-MS-Office365-Filtering-Correlation-Id: 7791439a-c926-4d5a-e94c-08ddc2ebc492 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|7416014|376014; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?LDs+dyukL24D88LL1+FyDyVwfiYePlS4NS02birOt6j5kAUyG9YARbGh7SEl?= =?us-ascii?Q?AaZWP8OpTFx4J1MvQl+hcGhhwfAgx8teLNgnek1E+ijswUBLbAJuvPR7ocF1?= =?us-ascii?Q?DXMqQvrjG5UBRh1mU5r1lrxMTMTwnWHxKTEhVuqqH0vmSstT2wiai2okEWBy?= =?us-ascii?Q?mfg7hACAQAJuh+OxUB4DORHzCszGiDthpviCgU8wGshP55h6acnA/zZ83Tq+?= =?us-ascii?Q?Bo//kxiz9VscvNqJFLncYJW6ALIyYEsz7LqNnK5V9pQbaKIk3G1syDc+xTGd?= =?us-ascii?Q?X8NfsQpersHifasvoMCn/1kBZu3hRIYYfFKjGawt8tquf6DwKdNlePs+wlTK?= =?us-ascii?Q?LSjsdsEAj59IzzhdSRgh3GxqopDeVm1o83kBxwkRjzYN2YsSuQs+1c/a65GY?= =?us-ascii?Q?TNd2T/PfKXGByMvstNaueGW2tbcj3CYcJN5sWWznYqsIEmdWIgnQD07Gokia?= =?us-ascii?Q?4O6P6zVaanIitsCmQiQQ8G8pzFFNXJoP+oWupkt6Ucpg1yLnWXP1KEQhrcSl?= =?us-ascii?Q?VtQqkRykJ25mchj65+WJSZznscRntM1ssZcyKsK403OSSBkAzPfzBTg5r7Xx?= =?us-ascii?Q?bZF+Z7jMqF3ua5sXzhY72A7MSvBbybN7OsYqs68KmDxLlRRjEUIF6dWBv7Wh?= =?us-ascii?Q?E00h7R4jRFs4FA64lkjp+zNGyHwkOGm7imExxD1NSgb5hKMW0ePQFwATbONd?= =?us-ascii?Q?J3e2V3cp7/zuFFNO5CRMKs/LlN8kWhutpE0uQUwYAx7bTXkiV2oxOFH+qYB0?= =?us-ascii?Q?VeY3/x/CJNkKGDSWVsZvVGca3PkBju5Qj/oxZfVQ60AYzoAwgQIBin+wZzeg?= =?us-ascii?Q?zHHJxAw0raubwGrJgQQ9GLJmIvLK0VPGSelkj0D0EQ7mn7/XuFYt3AQQP1GO?= =?us-ascii?Q?P2IuBQbP9jfbvp16e7Gb9y4ZZ9ndw5TSeMxfDMVacIdN7Zrvx+ItxZlZ2u1X?= =?us-ascii?Q?NjsRD8cwIw/yy1YBVYZmtOskXA0D6MMbG9PQ2Wxl0B/buxon9HEe496BIuCG?= =?us-ascii?Q?Y8uNhe9j/1sye4aluQClbnLJxEPTho/cH0aLonofz/xiaw8a1I1e9GwJXGWS?= =?us-ascii?Q?8cbNnvHQWUnSaBTlyx0IDpXq8IvKcY5gBrnjTmmHQU0e/x/TMz5pDnjP9J1G?= =?us-ascii?Q?Ujow0Ib0rl9bVBNViDOzTm+AEqiuEvxOH0DyQ26Dk5PYodggr+IJkTHAsrQe?= =?us-ascii?Q?J+RaNTrPXTTR955W8cWUMXFNGG5ysih1/X3GOtmoxx6AVVa/gp4hQx/8KZ9u?= =?us-ascii?Q?EJxi3b3wdA39SR7haiT1NuGCjEb5ZH5tCvYuisDYdqzEP63OIBew5A6mUxsV?= =?us-ascii?Q?iZOb5koNWNsLMvQQqU+xmb9rlhzZg/yV8AmJbkGwar1SNPqGXmpiojCRco/c?= =?us-ascii?Q?XENCZapzdsWsLkXAjg1u5BS+XpC2v6m+/S052mhjbfWIL2nf7b8LiY6bK/ah?= =?us-ascii?Q?wrpDxK2t7DgdWoJL7G7Jj+4Rhw1mXZcoW8p76tCponGNPUKg+PZnjsPFZgLG?= =?us-ascii?Q?BP//C8FYv6zCTh4GSPsQ0+kF49rr3Lt4zqNcd12N8EIW3viLQInm8UX/6eEN?= =?us-ascii?Q?HjxXIMzOEm6BaxbOEAOYhvkI9qaMlNyvdfA6XMRf?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 7791439a-c926-4d5a-e94c-08ddc2ebc492 X-MS-Exchange-CrossTenant-AuthSource: DS7PR12MB9473.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 14 Jul 2025 15:33:22.8600 (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: 3pT1a3rPlilX8h0T/9wQgZnAfQQjeiZ4BR+qsXkUJFlkaOEiQtfnTxDO1uiyMDRm X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM4PR12MB6184 On 14 Jul 2025, at 11:30, David Hildenbrand wrote: > On 11.07.25 20:23, Zi Yan wrote: >> remap(), folio_ref_unfreeze(), lru_add_split_folio() are not relevant = to >> splitting unmapped folio operations. Move them out to the caller so th= at >> __split_unmapped_folio() only handles unmapped folio splits. This make= s >> __split_unmapped_folio() reusable. >> >> Convert VM_BUG_ON(mapping) to use VM_WARN_ON_ONCE_FOLIO(). >> >> Signed-off-by: Zi Yan >> --- > > [...] > >> - if (folio_test_swapcache(folio)) { >> - VM_BUG_ON(mapping); >> - >> - /* a swapcache folio can only be uniformly split to order-0 */ >> - if (!uniform_split || new_order !=3D 0) >> - return -EINVAL; >> - >> - swap_cache =3D swap_address_space(folio->swap); >> - xa_lock(&swap_cache->i_pages); >> - } >> - >> if (folio_test_anon(folio)) >> mod_mthp_stat(order, MTHP_STAT_NR_ANON, -1); >> - /* lock lru list/PageCompound, ref frozen by page_ref_freeze */ >> - lruvec =3D folio_lruvec_lock(folio); >> > > Nit: now double empty line. Will fix it. > >> folio_clear_has_hwpoisoned(folio); >> @@ -3480,9 +3451,9 @@ static int __split_unmapped_folio(struct folio = *folio, int new_order, >> for (split_order =3D start_order; >> split_order >=3D new_order && !stop_split; >> split_order--) { >> - int old_order =3D folio_order(folio); >> - struct folio *release; >> struct folio *end_folio =3D folio_next(folio); >> + int old_order =3D folio_order(folio); >> + struct folio *new_folio; >> /* order-1 anonymous folio is not supported */ >> if (folio_test_anon(folio) && split_order =3D=3D 1) >> @@ -3517,113 +3488,34 @@ static int __split_unmapped_folio(struct foli= o *folio, int new_order, >> after_split: >> /* >> - * Iterate through after-split folios and perform related >> - * operations. But in buddy allocator like split, the folio >> + * Iterate through after-split folios and update folio stats. >> + * But in buddy allocator like split, the folio >> * containing the specified page is skipped until its order >> * is new_order, since the folio will be worked on in next >> * iteration. >> */ >> - for (release =3D folio; release !=3D end_folio; release =3D next) {= >> - next =3D folio_next(release); >> + for (new_folio =3D folio; new_folio !=3D end_folio; new_folio =3D n= ext) { >> + next =3D folio_next(new_folio); >> /* >> - * for buddy allocator like split, the folio containing >> - * page will be split next and should not be released, >> - * until the folio's order is new_order or stop_split >> - * is set to true by the above xas_split() failure. >> + * for buddy allocator like split, new_folio containing >> + * page could be split again, thus do not change stats >> + * yet. Wait until new_folio's order is new_order or >> + * stop_split is set to true by the above xas_split() >> + * failure. >> */ >> - if (release =3D=3D page_folio(split_at)) { >> - folio =3D release; >> + if (new_folio =3D=3D page_folio(split_at)) { >> + folio =3D new_folio; >> if (split_order !=3D new_order && !stop_split) >> continue; >> } >> - if (folio_test_anon(release)) { >> - mod_mthp_stat(folio_order(release), >> + if (folio_test_anon(new_folio)) { >> + mod_mthp_stat(folio_order(new_folio), >> MTHP_STAT_NR_ANON, 1); >> } > > Nit: {} can be dropped Sure. > > Code is still confusing, so could be that I miss something, but in gene= ral > looks like an improvement to me. > > I think we can easily get rid of the goto label in __split_unmapped_fol= io() doing something like > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 14bc0b54cf9f0..db0ae957a0ba8 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -3435,18 +3435,18 @@ static int __split_unmapped_folio(struct folio = *folio, int new_order, > if (xas_error(xas)) { > ret =3D xas_error(xas); > stop_split =3D true; > - goto after_split; > } > } > } > - folio_split_memcg_refs(folio, old_order, split_order);= > - split_page_owner(&folio->page, old_order, split_order);= > - pgalloc_tag_split(folio, old_order, split_order); > + if (!stop_split) { > + folio_split_memcg_refs(folio, old_order, split_= order); > + split_page_owner(&folio->page, old_order, split= _order); > + pgalloc_tag_split(folio, old_order, split_order= ); > - __split_folio_to_order(folio, old_order, split_order);= > + __split_folio_to_order(folio, old_order, split_= order); > + } > -after_split: > /* > * Iterate through after-split folios and update folio = stats. > * But in buddy allocator like split, the folio > Yep, looks much better to me. Let me fix it in V3. Thank you for the revi= ew and suggestions. Best Regards, Yan, Zi