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Howlett" , ankita@nvidia.com, aniketa@nvidia.com, vsethi@nvidia.com, mochs@nvidia.com, skolothumtho@nvidia.com, linmiaohe@huawei.com, nao.horiguchi@gmail.com, akpm@linux-foundation.org, david@redhat.com, lorenzo.stoakes@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, tony.luck@intel.com, bp@alien8.de, rafael@kernel.org, guohanjun@huawei.com, mchehab@kernel.org, lenb@kernel.org, kevin.tian@intel.com, alex@shazbot.org, cjia@nvidia.com, kwankhede@nvidia.com, targupta@nvidia.com, zhiw@nvidia.com, dnigam@nvidia.com, kjaju@nvidia.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-edac@vger.kernel.org, Jonathan.Cameron@huawei.com, ira.weiny@intel.com, Smita.KoralahalliChannabasappa@amd.com, u.kleine-koenig@baylibre.com, peterz@infradead.org, linux-acpi@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH v3 0/3] mm: Implement ECC handling for pfn with no struct page Message-ID: <20251021164444.GB699957@nvidia.com> References: <20251021102327.199099-1-ankita@nvidia.com> Content-Type: text/plain; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?bg35q5ht5xmIkQ5LCgykjLrwvO7/lNW0ncsqvLtlixTLVODt2wUr83N78PhH?= =?us-ascii?Q?lnQ6RmEFrulglGRX+zuFcUnUPMf3Ll6X62daG1KsxR4Sl9VrE3mZe6wOdo0A?= =?us-ascii?Q?ZbYxvyeQ4sNOK4KHsm+EgVdkXpOBk9slrfm+7gQTKky39FGZLTsVV2aWso5R?= =?us-ascii?Q?Pyo3UjKgYuCRKIX0UG732hSunlCHyQ6G61Ei9EmhCVN8LCNIg+aPiFArMF1N?= =?us-ascii?Q?5iSithVBJ82cfbdIgQgztjD9cV0lvyLhZqbTDsjAqnbJM6AZpb4RbNYvysnX?= =?us-ascii?Q?AMn6YCR72JREyvdMZeaT3Qv1PDOJtlrVUw0fErPRPMd6OASK8N8I6b+Xpwx5?= =?us-ascii?Q?mni8vALq8I9nKMy+cYQFhktZ3OJZFPBI2JtbC7QKpiyyj8TtX+28XB81lbXQ?= =?us-ascii?Q?kQt6Q5dFeQRAWM4d+8fFYZmNG4SM+AzVjBwUDlXNmPZYrIywMbln3t0S9Mid?= =?us-ascii?Q?7XSoSjnuE0Xi0wI1XOUw8NS7CMDZ71umC7PMMcmnAANz3v9waRbjbawoOgz+?= =?us-ascii?Q?dwke91KRcf4OrkiyziEbny/sRfXyWyBgDEINPd1hMcEzKhIRs7R5UfP8p9/0?= =?us-ascii?Q?0ygsWeBtp+XWPTCKEAv9ryXAEZdTADij/mRCCM7EshMMLuY9kiaAkrpQKUEF?= =?us-ascii?Q?s1vCQ36jAtmjMWcijaf8pEjpzLqplguaov4L3Xs5lmSKntea6WGX1sYuf6pn?= =?us-ascii?Q?OcE/zdy4BzRKB6XTVgTPcM4DB6rKtcNllhQW2wQNJLWeBz5Yfx+rJCpc0qa7?= =?us-ascii?Q?yd626cznJB1iOUn4MGPcYIZJcUZpdGGuU3HKp94db2c4WKzBQ7zPgJxTju+6?= =?us-ascii?Q?RPAHXtxGZc/LRs2TEwzmowXv5pJwSxgP2mwbwWUfIMiIx7RU2XgfLePHIRXk?= =?us-ascii?Q?YBpoxvrD7pXD3Xp9po1A39xLliL6zTQ5/TdhgSCgyUz72JVuxIg9uicIDI4I?= =?us-ascii?Q?C1A7eVCO5lot4AMAMQgRxiSn+o/lH6mYWuGCR+myAv7AzTwp18Ub+lXMA3sI?= =?us-ascii?Q?a4PEfQMTnFWfKKkILSivoYSMUdso1RCK4x2nKlwQtoi4Fvp77z8Fkqz/1bPj?= =?us-ascii?Q?4NnywcVhf2csaUJK2x2O3rJtzfRm90rKeP05OIT4LdRWWwOU0yyuNu4p5uMV?= =?us-ascii?Q?48UrMrxemlsiZTizc93f3rzWixKYo8TFihERo8oIHcleaH9pDb27/YUSb+da?= =?us-ascii?Q?Q9j4zFCvOSSjAEAHmdXs89V0F6xsnUFHncwoqP0GV2RJvgeO31UIssZyG2e3?= =?us-ascii?Q?u7moPJwEFj5vcPOyagaXO7Jn92NZZGZtXiGJkvJI2wcOTAbJjGOfiKq52Un2?= =?us-ascii?Q?zVHLCq/lSzi7l7TyJtzpwbSbhcvNrhJp+C8dcqXNp5chqxBDIWo6TxA8b/AQ?= =?us-ascii?Q?WW2LBOyxU3tOBQEMHiBAhBkWO8ZWiw+bRIrvno81DK6vQN1HWVrv1FYk3WaP?= =?us-ascii?Q?D5AXtlnx6K8KCQ55grT1vrzySultB7O1lB49NscrdbGLOZ6EHxqAS5hfZ72z?= =?us-ascii?Q?FpWNhENG8lJ9bp2QRxIh2cvu/4nNWJCn/ByMLl2gDTacNLEBIZVh3wGQGx8A?= =?us-ascii?Q?kQOIfeGUWcxZ55/ZKP9IBpM8j+6tNs2UALFFMMCn?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: ec39f1cf-d737-4659-f96e-08de10c1247c X-MS-Exchange-CrossTenant-AuthSource: BN8PR12MB3604.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 21 Oct 2025 16:44:46.5083 (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: IOBvRI6DnFjZBK6F5IKzBoeGrEFnobBLU3/CRUbTCV2EKyi4NSVEl+0+CoBhvUoj X-MS-Exchange-Transport-CrossTenantHeadersStamped: LV3PR12MB9186 On Tue, Oct 21, 2025 at 12:30:48PM -0400, Liam R. Howlett wrote: > > enables VM_PFNMAP vmas to map at PMD level. Otherwise, a poison to a PFN > > would need breaking the PMD mapping into PTEs to unmap only the poisoned > > PFN. This can have a major performance impact. > > Is the performance impact really a concern in the event of failed > memory? Yes, something like the KVM S2 is very sensitive to page size for TLB performace. > Does this happen enough to warrant this special case? If you have a 100k sized cluster it happens constantly :\ > Surely it's not failing hardware that may cause performance impacts, so > is this triggered in some other way that I'm missing or a conversation > pointer? It is the splitting of a pgd/pmd level into PTEs that gets mirrored into the S2 and then greatly increases the cost of table walks inside a guest. The HW caches are sized for 1G S2 PTEs, not 4k. Jason