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Although the code is designed to be generic when it comes >> to handling splitting of pages, the code is designed to work for THP >> page sizes corresponding to HPAGE_PMD_NR. >> >> Modify page_vma_mapped_walk() to return true when a zone device huge >> entry is present, enabling try_to_migrate() and other code migration >> paths to appropriately process the entry. page_vma_mapped_walk() will >> return true for zone device private large folios only when >> PVMW_THP_DEVICE_PRIVATE is passed. This is to prevent locations that are >> not zone device private pages from having to add awareness. The key >> callback that needs this flag is try_to_migrate_one(). The other >> callbacks page idle, damon use it for setting young/dirty bits, which is >> not significant when it comes to pmd level bit harvesting. >> >> pmd_pfn() does not work well with zone device entries, use >> pfn_pmd_entry_to_swap() for checking and comparison as for zone device >> entries. >> >> Support partial unmapping of zone device private entries, which happens >> via munmap(). munmap() causes the device private entry pmd to be split, >> but the corresponding folio is not split. Deferred split does not work for >> zone device private folios due to the need to split during fault >> handling. Get migrate_vma_collect_pmd() to handle this case by splitting >> partially unmapped device private folios. >> >> Cc: Andrew Morton >> Cc: David Hildenbrand >> Cc: Zi Yan >> Cc: Joshua Hahn >> Cc: Rakie Kim >> Cc: Byungchul Park >> Cc: Gregory Price >> Cc: Ying Huang >> Cc: Alistair Popple >> Cc: Oscar Salvador >> Cc: Lorenzo Stoakes >> Cc: Baolin Wang >> Cc: "Liam R. Howlett" >> Cc: Nico Pache >> Cc: Ryan Roberts >> Cc: Dev Jain >> Cc: Barry Song >> Cc: Lyude Paul >> Cc: Danilo Krummrich >> Cc: David Airlie >> Cc: Simona Vetter >> Cc: Ralph Campbell >> Cc: Mika Penttilä >> Cc: Matthew Brost >> Cc: Francois Dugast >> >> Signed-off-by: Matthew Brost >> Signed-off-by: Balbir Singh >> --- >> include/linux/rmap.h | 2 + >> include/linux/swapops.h | 17 ++++ >> lib/test_hmm.c | 2 +- >> mm/huge_memory.c | 214 +++++++++++++++++++++++++++++++--------- >> mm/migrate_device.c | 47 +++++++++ >> mm/page_vma_mapped.c | 13 ++- >> mm/pgtable-generic.c | 6 ++ >> mm/rmap.c | 24 ++++- >> 8 files changed, 272 insertions(+), 53 deletions(-) >> >> diff --git a/include/linux/rmap.h b/include/linux/rmap.h >> index 6cd020eea37a..dfb7aae3d77b 100644 >> --- a/include/linux/rmap.h >> +++ b/include/linux/rmap.h >> @@ -927,6 +927,8 @@ struct page *make_device_exclusive(struct mm_struct *mm, unsigned long addr, >> #define PVMW_SYNC (1 << 0) >> /* Look for migration entries rather than present PTEs */ >> #define PVMW_MIGRATION (1 << 1) >> +/* Look for device private THP entries */ >> +#define PVMW_THP_DEVICE_PRIVATE (1 << 2) >> >> struct page_vma_mapped_walk { >> unsigned long pfn; >> diff --git a/include/linux/swapops.h b/include/linux/swapops.h >> index 64ea151a7ae3..2641c01bd5d2 100644 >> --- a/include/linux/swapops.h >> +++ b/include/linux/swapops.h >> @@ -563,6 +563,7 @@ static inline int is_pmd_migration_entry(pmd_t pmd) >> { >> return is_swap_pmd(pmd) && is_migration_entry(pmd_to_swp_entry(pmd)); >> } >> + >> #else /* CONFIG_ARCH_ENABLE_THP_MIGRATION */ >> static inline int set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw, >> struct page *page) >> @@ -594,6 +595,22 @@ static inline int is_pmd_migration_entry(pmd_t pmd) >> } >> #endif /* CONFIG_ARCH_ENABLE_THP_MIGRATION */ >> >> +#if defined(CONFIG_ZONE_DEVICE) && defined(CONFIG_ARCH_ENABLE_THP_MIGRATION) >> + >> +static inline int is_pmd_device_private_entry(pmd_t pmd) >> +{ >> + return is_swap_pmd(pmd) && is_device_private_entry(pmd_to_swp_entry(pmd)); >> +} >> + >> +#else /* CONFIG_ZONE_DEVICE && CONFIG_ARCH_ENABLE_THP_MIGRATION */ >> + >> +static inline int is_pmd_device_private_entry(pmd_t pmd) >> +{ >> + return 0; >> +} >> + >> +#endif /* CONFIG_ZONE_DEVICE && CONFIG_ARCH_ENABLE_THP_MIGRATION */ >> + >> static inline int non_swap_entry(swp_entry_t entry) >> { >> return swp_type(entry) >= MAX_SWAPFILES; >> diff --git a/lib/test_hmm.c b/lib/test_hmm.c >> index 761725bc713c..297f1e034045 100644 >> --- a/lib/test_hmm.c >> +++ b/lib/test_hmm.c >> @@ -1408,7 +1408,7 @@ static vm_fault_t dmirror_devmem_fault(struct vm_fault *vmf) >> * the mirror but here we use it to hold the page for the simulated >> * device memory and that page holds the pointer to the mirror. >> */ >> - rpage = vmf->page->zone_device_data; >> + rpage = folio_page(page_folio(vmf->page), 0)->zone_device_data; >> dmirror = rpage->zone_device_data; >> >> /* FIXME demonstrate how we can adjust migrate range */ >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index 9c38a95e9f09..2495e3fdbfae 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c >> @@ -1711,8 +1711,11 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm, >> if (unlikely(is_swap_pmd(pmd))) { >> swp_entry_t entry = pmd_to_swp_entry(pmd); >> >> - VM_BUG_ON(!is_pmd_migration_entry(pmd)); >> - if (!is_readable_migration_entry(entry)) { >> + VM_WARN_ON(!is_pmd_migration_entry(pmd) && >> + !is_pmd_device_private_entry(pmd)); >> + >> + if (is_migration_entry(entry) && >> + is_writable_migration_entry(entry)) { >> entry = make_readable_migration_entry( >> swp_offset(entry)); >> pmd = swp_entry_to_pmd(entry); >> @@ -1722,6 +1725,32 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm, >> pmd = pmd_swp_mkuffd_wp(pmd); >> set_pmd_at(src_mm, addr, src_pmd, pmd); >> } >> + >> + if (is_device_private_entry(entry)) { >> + if (is_writable_device_private_entry(entry)) { >> + entry = make_readable_device_private_entry( >> + swp_offset(entry)); >> + pmd = swp_entry_to_pmd(entry); >> + >> + if (pmd_swp_soft_dirty(*src_pmd)) >> + pmd = pmd_swp_mksoft_dirty(pmd); >> + if (pmd_swp_uffd_wp(*src_pmd)) >> + pmd = pmd_swp_mkuffd_wp(pmd); >> + set_pmd_at(src_mm, addr, src_pmd, pmd); >> + } >> + >> + src_folio = pfn_swap_entry_folio(entry); >> + VM_WARN_ON(!folio_test_large(src_folio)); >> + >> + folio_get(src_folio); >> + /* >> + * folio_try_dup_anon_rmap_pmd does not fail for >> + * device private entries. >> + */ >> + VM_WARN_ON(folio_try_dup_anon_rmap_pmd(src_folio, >> + &src_folio->page, dst_vma, src_vma)); > > VM_WARN_ON compiles out in non-debug builds. I hit this running the > fork self I shared with a non-debug build. folio_try_dup_anon_rmap_pmd() will never fail for folio_is_device_private(folio) -- unless something is deeply messed up that we wouldn't identify this folio as being device-private. Can you elaborate, what were you able to trigger, and in what kind of environment? -- Cheers David / dhildenb