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Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , Usama Arif , Kiryl Shutsemau , Peter Xu , Alex Williamson , kvm@vger.kernel.org, =?UTF-8?Q?Lo=C3=AFc_Molinari?= , Lorenzo Stoakes , Shuah Khan , linux-kselftest@vger.kernel.org, dri-devel@lists.freedesktop.org, Madhavan Srinivasan , "Ritesh Harjani (IBM)" , linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Jason Gunthorpe References: <20261021-b4-prep-vstor-149847-copy_huge_pmd-recheck-special-pmd-v4-0-66f00b7a564c@virtuozzo.com> <20261021-b4-prep-vstor-149847-copy_huge_pmd-recheck-special-pmd-v4-1-66f00b7a564c@virtuozzo.com> <8C082879-C8F6-475D-9460-DF5E3CB629E4@nvidia.com> Content-Language: en-US, ru, sr From: Konstantin Khorenko In-Reply-To: <8C082879-C8F6-475D-9460-DF5E3CB629E4@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: AS4PR10CA0007.EURPRD10.PROD.OUTLOOK.COM (2603:10a6:20b:5dc::9) To PA6PR08MB10708.eurprd08.prod.outlook.com (2603:10a6:102:3c7::20) X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PA6PR08MB10708:EE_|MI7PR08MB884834:EE_ X-MS-Office365-Filtering-Correlation-Id: 249f093b-bd4f-49c2-de76-08df30280ffa X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|376014|366016|23010399003|1800799024|10067099003|22082099003|18002099003|261021121427099003|261021123027099003|261009223027099003|4143699003|56012099006; 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Each unmap of the > > >> PMD removes one PMD mapping: >> >> - the folio's mapcount never returns to zero, and removing the folio >> from the page cache reports "Bad page cache", or hits a VM_BUG_ON >> with CONFIG_DEBUG_VM; >> - the first unmap already counts as the last one and drops the >> PMD-mapped statistics while the other mm still maps the folio; >> - the second one drives the entire mapcount below zero and drops them >> again. > > This chunk of text probably can go away, since no one is affected > by the code. Sure, will drop it once we are ready for the next iteration. Thank you! >> The helper has no caller yet, the next patch adds the first one. Pass >> PGTABLE_LEVEL_PMD, as folio_try_dup_anon_rmap_pmd() does. >> >> Fixes: d8ef5e311d7b ("mm/rmap: convert page_dup_file_rmap() to folio_dup_file_rmap_[pte|ptes|pmd]()") >> Signed-off-by: Konstantin Khorenko >> --- >> include/linux/rmap.h | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> > > The code change looks good to me. I also find this when I am working > on PG_folio. Thanks. > > Reviewed-by: Zi Yan > > > Best Regards, > Yan, Zi