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[PATCH] mm/migrate: wake kcompactd when huge folio migration fails in numa balancing Cc: "Andrew Morton" , "David Hildenbrand" , "Matthew Brost" , "Byungchul Park" , "Ying Huang" , "Alistair Popple" , , , To: "Joshua Hahn" , "Gregory Price" From: "Zi Yan" X-Mailer: aerc 0.22.0 References: <20261022172547.1181530-1-joshua.hahnjy@gmail.com> In-Reply-To: <20261022172547.1181530-1-joshua.hahnjy@gmail.com> X-ClientProxiedBy: YQZPR01CA0015.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:c01:85::20) To IA0PR12MB8374.namprd12.prod.outlook.com (2603:10b6:208:40e::7) X-Archived-By: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: IA0PR12MB8374:EE_|DS7PR12MB9503:EE_ X-MS-Office365-Filtering-Correlation-Id: b3932136-b231-4484-f915-08df306e936d X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: 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 6bZ5sfiR HOogqJPRueyvSxo/jUM1qCGaX5wBgrq3H4OQfOgJXOIrb1ksGMlMt+ZEoED7ky9iS9apHpHU9glhDCeoNl2zzsslx0n1YzpaYVtMgHmDHeEKqXHl3nli8bhOz97mqXAkbsYLoXQ/JpZXFXfZWgXHvOpxOuDA4U4pLj1eB4WbyDnzKAkFCQ2e02U29EQwHwkyGogkJvwbBxFLwYYabl4odBxDcFvTsXXeXM8zMQ27KIEYXW+Fpq1R8h1R4ewt4vCz7Sl4Pvhr1ExvBFLwG64heGcZYSizjN5pI+G9vMVjLGU0Vw4enORRb58pqSFxpRGNXJjByDH8yMlmCTFO3tkYSf0Eakrt43gmPZWUL+KuxSZxMdJIGkQoEiSxeeks0P0PUpt7SS9zKp0eOhw1GWTroVhvoD3jhzexut+j+KJspfHX/s/0CkV8XtJHY3rBEF7VNRotelMtR7RgXf5GkINRNctEnLHVKIA25cbr8 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Thu Oct 22, 2026 at 1:25 PM EDT, Joshua Hahn wrote: > NUMA balancing migrates a misplaced folio if migrate_balanced_pgdat() > finds enough headroom on the destination node. For large folios, it then > allocates a folio from the destination with GFP_TRANSHUGE_LIGHT, which > wakes up neither kswapd nor kcompactd. This means a hot large folio > trying to promote to a fragmented destination may never succeed in > promotion even after repeated retries. > > Wake kcompactd on the target node when the destination allocation fails > for a large folio. Don't wake kswapd, since this path can only be > reached if there is enough free memory to service the allocation, but it > is too fragmented to serve the large folio allocation. > > This patch has been A/B tested on tiered Meta systems (DRAM + CXL) > running identical cacheing workloads. Without this patch, we accumulate > around 4.5k failed THP migrations over the span of a day, while the host > with this patch accumulates only about 80. Is proactive compaction enabled? If yes, why does it not help? > > Those migration differences leads to about 25% reduced CXL bandwidth > usage after applying this patch. > > Signed-off-by: Joshua Hahn > --- > mm/migrate.c | 13 ++++++++++++- > 1 file changed, 12 insertions(+), 1 deletion(-) > > diff --git a/mm/migrate.c b/mm/migrate.c > index 7bdcdb57652f8..67364fe0851c0 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -2671,6 +2671,7 @@ static struct folio *alloc_misplaced_dst_folio(stru= ct folio *src, > int nid =3D (int) data; > int order =3D folio_order(src); > gfp_t gfp =3D __GFP_THISNODE; > + struct folio *dst; > =20 > if (order > 0) > gfp |=3D GFP_TRANSHUGE_LIGHT; > @@ -2679,7 +2680,17 @@ static struct folio *alloc_misplaced_dst_folio(str= uct folio *src, > __GFP_NOWARN; > gfp &=3D ~__GFP_RECLAIM; > } > - return __folio_alloc_node(gfp, order, nid); > + > + dst =3D __folio_alloc_node(gfp, order, nid); > + > + /* > + * A node with enough free memory might still be too fragmented to serv= e > + * a large folio. Wake kcompactd to help the next huge folio migration. > + */ > + if (!dst && order > 0) > + wakeup_kcompactd(NODE_DATA(nid), order, gfp_zone(gfp)); > + > + return dst; > } > =20 > /* --=20 Best Regards, Yan, Zi