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Howlett" , "Mike Rapoport" , , To: "Johannes Weiner" , "Andrew Morton" , "Vlastimil Babka" From: "Zi Yan" X-Mailer: aerc 0.21.0 References: <20260626182215.1107966-1-hannes@cmpxchg.org> <20260626182215.1107966-3-hannes@cmpxchg.org> In-Reply-To: <20260626182215.1107966-3-hannes@cmpxchg.org> X-ClientProxiedBy: MN2PR22CA0020.namprd22.prod.outlook.com (2603:10b6:208:238::25) To IA0PR12MB8374.namprd12.prod.outlook.com (2603:10b6:208:40e::7) 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: IA0PR12MB8374:EE_|LV2PR12MB5846:EE_ X-MS-Office365-Filtering-Correlation-Id: 2a131427-f19e-49ef-fe21-08ded7dbdbcc X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|23010399003|376014|7416014|22082099003|18002099003|4143699003|56012099006|11063799006; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:IA0PR12MB8374.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(1800799024)(366016)(23010399003)(376014)(7416014)(22082099003)(18002099003)(4143699003)(56012099006)(11063799006);DIR:OUT;SFP:1101; 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This is to prevent migratetype > pollution, where a small non-movable request frees space in a movable > block and provokes the allocator to fall back and pollute it. > > This protection is reasonable on one hand, but the downside is that it > makes non-movable direct compaction nearly useless: if we get the type > annotations right, by definition there aren't any movable pages inside > the non-movable blocks it is allowed to scan. > > With defrag_mode, the goal is the production of whole blocks, which > are essentially type neutral: __rmqueue_claim() will convert them > wholesale on alloc. This makes type mixing and pollution a non-issue. > > Fix the pollution gates to take the requested order into account, and > allow whole-block requests to scan blocks of other types. > > The only exception is CMA blocks. That type is sticky and these blocks > cannot be claimed to other types. Continue to be strict with them, and > allow only explicit ALLOC_CMA requests and kcompactd to evacuate them. > > Signed-off-by: Johannes Weiner > --- > mm/compaction.c | 35 ++++++++++++++++++++++++++++------- > 1 file changed, 28 insertions(+), 7 deletions(-) > > + > + /* > + * Prevent small unmovable/reclaimable requests from polluting "small" here means smaller than pageblock_order requests? If yes, it is better to spell it out to prevent confusion. > + * movable blocks through fallbacks. Whole-block production is > + * exempt as the allocator claims and converts these. > + */ > + if (cc->migratetype =3D=3D MIGRATE_MOVABLE || cc->order >=3D pageblock_= order) > return is_migrate_movable(block_mt); > else > return block_mt =3D=3D cc->migratetype; > @@ -1974,12 +1995,12 @@ static unsigned long fast_find_migrateblock(struc= t compact_control *cc) > return pfn; > =20 > /* > - * Only allow kcompactd and direct requests for movable pages to > - * quickly clear out a MOVABLE pageblock for allocation. This > - * reduces the risk that a large movable pageblock is freed for > - * an unmovable/reclaimable small allocation. > + * Prevent small unmovable/reclaimable requests from polluting This "small" as well. > + * movable blocks through fallbacks. Whole-block production is > + * exempt as the allocator claims and converts these. > */ > - if (cc->direct_compaction && cc->migratetype !=3D MIGRATE_MOVABLE) > + if (cc->direct_compaction && cc->migratetype !=3D MIGRATE_MOVABLE && > + cc->order < pageblock_order) > return pfn; > =20 > /* --=20 Best Regards, Yan, Zi