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Subject: Re: [PATCH v8 15/30] mm: swap in PMD swap entries as whole THPs during swapoff Cc: , "Baoquan He" , , , , , , , , , , , "Nico Pache" , "Liam R.Howlett" , , "Vlastimil Babka" , , , , , , , , To: "Usama Arif" , "Andrew Morton" , , , , , X-Mailer: aerc 0.22.0 References: <20261002095503.3585565-1-usama.arif@linux.dev> <20261002095503.3585565-16-usama.arif@linux.dev> In-Reply-To: <20261002095503.3585565-16-usama.arif@linux.dev> X-ClientProxiedBy: BN9PR03CA0297.namprd03.prod.outlook.com (2603:10b6:408:f5::32) To IA0PR12MB8374.namprd12.prod.outlook.com (2603:10b6:208:40e::7) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: IA0PR12MB8374:EE_|MW6PR12MB8760:EE_ X-MS-Office365-Filtering-Correlation-Id: 282fbff5-acdc-429b-bdad-08df2638ccb5 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|376014|7416014|23010399003|22082099003|18002099003|56012099006|11063799006|4143699003|10067099003; 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 vfcwhFc/ 4rjHHOymjtb6r07vzMa5Mj0AwIsbh4INXMB1frdxigfEmpSqYlO4kSu4AKQ2vvQxTt1yomAT8lco8W/ivYoN/fXPd6C0jG1JYDzCmAjyay4KxtRKEEKdy8MCJ7YG4UMnkpTDqxj6+jtJo0ZHPTgNESwVC0cAWWF0hRbodzN+Tf9fltyDcjJGaUzWqdTvX9QRA6KNtQ0B88M5+y0B60ubSIZPXNDqGkjOHhxaCHUQ93cHOhvW1jK2qa7AyCmGwHKYbQ2UcJsiu77wUQkbrcPTdMYw+SHM/S4apfGJ8TUfGCzwKx2TiP2yB8FbeMfzSj/HOVRZyE+agF7nLgvXvgJ1XTy7xVmQmjqUlU79dQy573nK/RkX/pA8VrNJqbg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri Oct 2, 2026 at 5:52 AM EDT, Usama Arif wrote: > swapoff walks every mm and faults every slot of the device back in. > unuse_pte_range() only understands PTEs, so a PMD swap entry would never = be > found and swapoff would never complete. > > A PMD swap entry is a compact encoding for HPAGE_PMD_NR slots, not a > promise that the swap cache holds one folio for them. Add > swap_pmd_cache_lookup() to classify the covered range as empty, one > PMD-sized folio, or already split, and unuse_pmd() to map the first two > cases back in as one THP, preserving soft-dirty, exclusive and UFFD state= . > > Everything else falls back to PTEs: a split cache, per-page zswap state, = a > failed PMD-order allocation or read, or a poisoned subpage. Check > PageHWPoison on every subpage rather than the folio-level flag, which > memory_failure() only sets after taking the folio lock. > > All the fallback reasons are observed without the PMD lock and possibly > after sleeping, so they share one exit that re-checks the PMD is still th= e > entry we were called for before splitting it. That exit also drops a foli= o > that is not uptodate, or that has never been mapped, from the swap cache: > the PTE path cannot re-read the first, and would add a single-page rmap t= o > the second. > > Signed-off-by: Usama Arif > --- > mm/internal.h | 16 ++++ > mm/swap.h | 17 +++++ > mm/swap_state.c | 44 +++++++++++ > mm/swapfile.c | 189 ++++++++++++++++++++++++++++++++++++++++++++++++ > 4 files changed, 266 insertions(+) > > diff --git a/mm/internal.h b/mm/internal.h > index 05179c4b2090e..ec7f007bc2c0d 100644 > --- a/mm/internal.h > +++ b/mm/internal.h > @@ -24,6 +24,22 @@ > =20 > struct folio_batch; > =20 > +/* A high level description like below might be better. Check every page in a folio for HWPoison flag. Return true if there is any. > + * Unlike folio_contain_hwpoisoned_page(), this does not rely on the fol= io-level > + * PG_has_hwpoisoned, which memory_failure() only sets after taking the = folio > + * lock and so can lag a tail-page poison. > + */ > +static inline bool folio_has_hwpoisoned_subpage(const struct folio *foli= o) s/subpage/page, IIRC, we are moving away from subpage. Maybe folio_has_any_hwpoisoned_page()? > +{ > + long nr =3D folio_nr_pages(folio); > + long i; > + > + for (i =3D 0; i < nr; i++) > + if (PageHWPoison(folio_page(folio, i))) > + return true; > + return false; > +} > + --=20 Best Regards, Yan, Zi