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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?svpJJf0g//ldq5Ulq9P0jlYpHg2swwG6yik85HAroeIY60mCMZYhChhI9Xnh?= =?us-ascii?Q?BMW+zoVo0p4Ntuh6TuxL2BkguVt+8dSxXSqYrm5G7QSUR2swfYyT/N8sCfoS?= =?us-ascii?Q?LJsppLz65gg+NiQ1kj7y4hz7SLkP/SYFSYyFYY5g5vKxrNX5BMTCTmSnqolK?= =?us-ascii?Q?tCR44OuHAIB8cZwZTSNpmlkVIPt0OpLAmOZMsLq4ZwQHNDh8kvNndq95DIAl?= =?us-ascii?Q?o4j1VNChsiiAgavljsqeHZiP+Yy4YObpooNkHJoXmjC2XMWEsze7Dv/3Yq7a?= =?us-ascii?Q?0gmGPvRLq+e0hsfLRbSe7f2jAh6fZEPZbPE3cxePGZvv+ZN/Ruuag6Zw1L+V?= =?us-ascii?Q?aTqxFGUpvNJai41wclKAyG7JxzGmBCscKCCXRls1Qeu74QMNpMwOnSwt2tHp?= =?us-ascii?Q?1648L9N0ArVkmPGFEGri7dMI/O6NZ5hFr3l2eh4luH6Vx4rLTy3AxRMperZa?= =?us-ascii?Q?2sDNa61uMsoE1vtApRraZtRIBtQzEnzCC+UbcgWJI4sOpYoRGbbAryc+IdM+?= =?us-ascii?Q?vzMv86TJ0o+l2BR4xI5zo9X/Pk8Xuu+vek1OwD+aMZzphukDVh4EFMauN9RP?= =?us-ascii?Q?lz+N0kwnrizbrij+4H/OMWrUfoTzGBHWQYtIt5hIxPovg7ywyAK/OH/220DW?= =?us-ascii?Q?as3fUGn/1LOZLItMoaKs1m1u1Xv8T4UaGLF/aVdbryzLsN48P2zjiOUQYKQ0?= =?us-ascii?Q?2QKOeuafrmogRl/4EWK+kw9GktUlp20Z4lGJz3AuBLxtfiFWUR9i1L7zTi5f?= =?us-ascii?Q?olOFST8l1fIxILct8QU4EIG70V/scp828XQO9xqI7f8FcSiKZKgL4d1DMoux?= =?us-ascii?Q?mfSfnvbd/5K7qHTbeGkOPBDyS+b69wydZVYGGcPJu0swu65tv/ILHs5+JzwT?= =?us-ascii?Q?iimfKIdtLNJ62uEpsNr9afU5VRMM9werXvjb8HxmwuMe5S4+BCdjKAaHJ2ax?= =?us-ascii?Q?VGzhI+NtT2csDtPq9Kaw0ofmeozc6m3YwtVdKbB/3Q92aG/PK8oFTFrRhO0m?= =?us-ascii?Q?7Cf8mJRdakUb1T04g0Yom5i+kBjTxaRiovIYGsrCsZG7T07w2y+fMA6D5VfJ?= =?us-ascii?Q?L8+DY7SsjMT9eHY4kQO2DmiahbeJ/QRwhVfiSk82tG/quGGmrboprJOCD0ey?= =?us-ascii?Q?gpFzItYO0pqXpmIlxYfFwD5RZ3crHwL0T5dzhZuykV4gnPLWW4SOy6LxTEKP?= =?us-ascii?Q?SlwYBRI9JuHAo91KukLmkcBaFKmWI1t2JLU95ENIfhkYtpAfgmyVRfU+yCq5?= =?us-ascii?Q?V9WXQngacJP21dqY0eMT6PPrYUGYiMw14EJNPTW+qh5CMSiKVZMrpOYTSFEZ?= =?us-ascii?Q?fsjfKSrzD7WhHr0CytAhumPa3VLF4WK7J/US2qFiuJp6W+VkwvhUnvtDJve/?= =?us-ascii?Q?0ED0U1yh9aE4BDoIzisloOBi42uOQaqS/NFTGon1HBaYCWvbVFmqYGYaoiH6?= =?us-ascii?Q?aowYYRmGzCOwPtQCmYM210soKyVSnb4JG1yLcyYNjDoPNeejn6S/Och3b9mH?= =?us-ascii?Q?/uERf5JWmJlk8pwaILYQMtf8hIKWRE5TI0IQuelbhaiX/df+pzr39+q/mhcc?= =?us-ascii?Q?F5CLBUiwQZw0QnqV2LyHXHJA1zWSgmd3OXcq10aw?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 6b6f4668-35ee-4d91-6f9a-08dcf38377c3 X-MS-Exchange-CrossTenant-AuthSource: DS7PR12MB9473.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 23 Oct 2024 16:55:15.6538 (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: KahIHPSsbA79D80mZA8EgFenkeY2oqHvV6K42rdCnIx6NFzCWpV8SaDJdlJYbdvZ X-MS-Exchange-Transport-CrossTenantHeadersStamped: IA1PR12MB9468 --=_MailMate_BC814CCE-22FE-4FED-BCC5-E9F36F03855E_= Content-Type: text/plain Content-Transfer-Encoding: quoted-printable On 23 Oct 2024, at 12:50, Usama Arif wrote: > On 23/10/2024 17:21, Zi Yan wrote: >> On 30 Aug 2024, at 6:03, Usama Arif wrote: >> >>> From: Yu Zhao >>> >>> Here being unused means containing only zeros and inaccessible to >>> userspace. When splitting an isolated thp under reclaim or migration,= >>> the unused subpages can be mapped to the shared zeropage, hence savin= g >>> memory. This is particularly helpful when the internal >>> fragmentation of a thp is high, i.e. it has many untouched subpages. >>> >>> This is also a prerequisite for THP low utilization shrinker which wi= ll >>> be introduced in later patches, where underutilized THPs are split, a= nd >>> the zero-filled pages are freed saving memory. >>> >>> Signed-off-by: Yu Zhao >>> Tested-by: Shuang Zhai >>> Signed-off-by: Usama Arif >>> --- >>> include/linux/rmap.h | 7 ++++- >>> mm/huge_memory.c | 8 ++--- >>> mm/migrate.c | 72 ++++++++++++++++++++++++++++++++++++++----= -- >>> mm/migrate_device.c | 4 +-- >>> 4 files changed, 75 insertions(+), 16 deletions(-) >>> >>> diff --git a/include/linux/rmap.h b/include/linux/rmap.h >>> index 91b5935e8485..d5e93e44322e 100644 >>> --- a/include/linux/rmap.h >>> +++ b/include/linux/rmap.h >>> @@ -745,7 +745,12 @@ int folio_mkclean(struct folio *); >>> int pfn_mkclean_range(unsigned long pfn, unsigned long nr_pages, pgo= ff_t pgoff, >>> struct vm_area_struct *vma); >>> >>> -void remove_migration_ptes(struct folio *src, struct folio *dst, boo= l locked); >>> +enum rmp_flags { >>> + RMP_LOCKED =3D 1 << 0, >>> + RMP_USE_SHARED_ZEROPAGE =3D 1 << 1, >>> +}; >>> + >>> +void remove_migration_ptes(struct folio *src, struct folio *dst, int= flags); >>> >>> /* >>> * rmap_walk_control: To control rmap traversing for specific needs >>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >>> index 0c48806ccb9a..af60684e7c70 100644 >>> --- a/mm/huge_memory.c >>> +++ b/mm/huge_memory.c >>> @@ -3020,7 +3020,7 @@ bool unmap_huge_pmd_locked(struct vm_area_struc= t *vma, unsigned long addr, >>> return false; >>> } >>> >>> -static void remap_page(struct folio *folio, unsigned long nr) >>> +static void remap_page(struct folio *folio, unsigned long nr, int fl= ags) >>> { >>> int i =3D 0; >>> >>> @@ -3028,7 +3028,7 @@ static void remap_page(struct folio *folio, uns= igned long nr) >>> if (!folio_test_anon(folio)) >>> return; >>> for (;;) { >>> - remove_migration_ptes(folio, folio, true); >>> + remove_migration_ptes(folio, folio, RMP_LOCKED | flags); >>> i +=3D folio_nr_pages(folio); >>> if (i >=3D nr) >>> break; >>> @@ -3240,7 +3240,7 @@ static void __split_huge_page(struct page *page= , struct list_head *list, >>> >>> if (nr_dropped) >>> shmem_uncharge(folio->mapping->host, nr_dropped); >>> - remap_page(folio, nr); >>> + remap_page(folio, nr, PageAnon(head) ? RMP_USE_SHARED_ZEROPAGE : 0)= ; >>> >>> /* >>> * set page to its compound_head when split to non order-0 pages, s= o >>> @@ -3542,7 +3542,7 @@ int split_huge_page_to_list_to_order(struct pag= e *page, struct list_head *list, >>> if (mapping) >>> xas_unlock(&xas); >>> local_irq_enable(); >>> - remap_page(folio, folio_nr_pages(folio)); >>> + remap_page(folio, folio_nr_pages(folio), 0); >>> ret =3D -EAGAIN; >>> } >>> >>> diff --git a/mm/migrate.c b/mm/migrate.c >>> index 6f9c62c746be..d039863e014b 100644 >>> --- a/mm/migrate.c >>> +++ b/mm/migrate.c >>> @@ -204,13 +204,57 @@ bool isolate_folio_to_list(struct folio *folio,= struct list_head *list) >>> return true; >>> } >>> >>> +static bool try_to_map_unused_to_zeropage(struct page_vma_mapped_wal= k *pvmw, >>> + struct folio *folio, >>> + unsigned long idx) >>> +{ >>> + struct page *page =3D folio_page(folio, idx); >>> + bool contains_data; >>> + pte_t newpte; >>> + void *addr; >>> + >>> + VM_BUG_ON_PAGE(PageCompound(page), page); >> >> This should be: >> >> diff --git a/mm/migrate.c b/mm/migrate.c >> index e950fd62607f..7ffdbe078aa7 100644 >> --- a/mm/migrate.c >> +++ b/mm/migrate.c >> @@ -206,7 +206,8 @@ static bool try_to_map_unused_to_zeropage(struct p= age_vma_mapped_walk *pvmw, >> pte_t newpte; >> void *addr; >> >> - VM_BUG_ON_PAGE(PageCompound(page), page); >> + if (PageCompound(page)) >> + return false; >> VM_BUG_ON_PAGE(!PageAnon(page), page); >> VM_BUG_ON_PAGE(!PageLocked(page), page); >> VM_BUG_ON_PAGE(pte_present(*pvmw->pte), page); >> >> Otherwise, splitting anonymous large folios to non order-0 ones just >> triggers this BUG_ON. >> > > That makes sense, would you like to send the fix? > > Adding Yu Zhao to "To" incase he has any objections. > Sure, will do. 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