On 9/11/25 21:52, Mika Penttilä wrote: > sending again for the v5 thread.. > > On 9/8/25 03:04, Balbir Singh wrote: > >> MIGRATE_VMA_SELECT_COMPOUND will be used to select THP pages during >> migrate_vma_setup() and MIGRATE_PFN_COMPOUND will make migrating >> device pages as compound pages during device pfn migration. >> >> migrate_device code paths go through the collect, setup >> and finalize phases of migration. >> >> The entries in src and dst arrays passed to these functions still >> remain at a PAGE_SIZE granularity. When a compound page is passed, >> the first entry has the PFN along with MIGRATE_PFN_COMPOUND >> and other flags set (MIGRATE_PFN_MIGRATE, MIGRATE_PFN_VALID), the >> remaining entries (HPAGE_PMD_NR - 1) are filled with 0's. This >> representation allows for the compound page to be split into smaller >> page sizes. >> >> migrate_vma_collect_hole(), migrate_vma_collect_pmd() are now THP >> page aware. Two new helper functions migrate_vma_collect_huge_pmd() >> and migrate_vma_insert_huge_pmd_page() have been added. >> >> migrate_vma_collect_huge_pmd() can collect THP pages, but if for >> some reason this fails, there is fallback support to split the folio >> and migrate it. >> >> migrate_vma_insert_huge_pmd_page() closely follows the logic of >> migrate_vma_insert_page() >> >> Support for splitting pages as needed for migration will follow in >> later patches in this series. >> >> Cc: Andrew Morton <[email protected]> >> Cc: David Hildenbrand <[email protected]> >> Cc: Zi Yan <[email protected]> >> Cc: Joshua Hahn <[email protected]> >> Cc: Rakie Kim <[email protected]> >> Cc: Byungchul Park <[email protected]> >> Cc: Gregory Price <[email protected]> >> Cc: Ying Huang <[email protected]> >> Cc: Alistair Popple <[email protected]> >> Cc: Oscar Salvador <[email protected]> >> Cc: Lorenzo Stoakes <[email protected]> >> Cc: Baolin Wang <[email protected]> >> Cc: "Liam R. Howlett" <[email protected]> >> Cc: Nico Pache <[email protected]> >> Cc: Ryan Roberts <[email protected]> >> Cc: Dev Jain <[email protected]> >> Cc: Barry Song <[email protected]> >> Cc: Lyude Paul <[email protected]> >> Cc: Danilo Krummrich <[email protected]> >> Cc: David Airlie <[email protected]> >> Cc: Simona Vetter <[email protected]> >> Cc: Ralph Campbell <[email protected]> >> Cc: Mika Penttilä <[email protected]> >> Cc: Matthew Brost <[email protected]> >> Cc: Francois Dugast <[email protected]> >> >> Signed-off-by: Balbir Singh <[email protected]> >> --- >> include/linux/migrate.h | 2 + >> mm/migrate_device.c | 456 ++++++++++++++++++++++++++++++++++------ >> 2 files changed, 395 insertions(+), 63 deletions(-) >> >> diff --git a/include/linux/migrate.h b/include/linux/migrate.h >> index 1f0ac122c3bf..41b4cc05a450 100644 >> --- a/include/linux/migrate.h >> +++ b/include/linux/migrate.h >> @@ -125,6 +125,7 @@ static inline int migrate_misplaced_folio(struct folio >> *folio, int node) >> #define MIGRATE_PFN_VALID (1UL << 0) >> #define MIGRATE_PFN_MIGRATE (1UL << 1) >> #define MIGRATE_PFN_WRITE (1UL << 3) >> +#define MIGRATE_PFN_COMPOUND (1UL << 4) >> #define MIGRATE_PFN_SHIFT 6 >> >> static inline struct page *migrate_pfn_to_page(unsigned long mpfn) >> @@ -143,6 +144,7 @@ enum migrate_vma_direction { >> MIGRATE_VMA_SELECT_SYSTEM = 1 << 0, >> MIGRATE_VMA_SELECT_DEVICE_PRIVATE = 1 << 1, >> MIGRATE_VMA_SELECT_DEVICE_COHERENT = 1 << 2, >> + MIGRATE_VMA_SELECT_COMPOUND = 1 << 3, >> }; >> >> struct migrate_vma { >> diff --git a/mm/migrate_device.c b/mm/migrate_device.c >> index f45ef182287d..1dfcf4799ea5 100644 >> --- a/mm/migrate_device.c >> +++ b/mm/migrate_device.c >> @@ -14,6 +14,7 @@ >> #include <linux/pagewalk.h> >> #include <linux/rmap.h> >> #include <linux/swapops.h> >> +#include <linux/pgalloc.h> >> #include <asm/tlbflush.h> >> #include "internal.h" >> >> @@ -44,6 +45,23 @@ static int migrate_vma_collect_hole(unsigned long start, >> if (!vma_is_anonymous(walk->vma)) >> return migrate_vma_collect_skip(start, end, walk); >> >> + if (thp_migration_supported() && >> + (migrate->flags & MIGRATE_VMA_SELECT_COMPOUND) && >> + (IS_ALIGNED(start, HPAGE_PMD_SIZE) && >> + IS_ALIGNED(end, HPAGE_PMD_SIZE))) { >> + migrate->src[migrate->npages] = MIGRATE_PFN_MIGRATE | >> + MIGRATE_PFN_COMPOUND; >> + migrate->dst[migrate->npages] = 0; >> + migrate->npages++; >> + migrate->cpages++; >> + >> + /* >> + * Collect the remaining entries as holes, in case we >> + * need to split later >> + */ >> + return migrate_vma_collect_skip(start + PAGE_SIZE, end, walk); >> + } >> + > > seems you have to split_huge_pmd() for the huge zero page here in case > of !thp_migration_supported() afaics >
Not really, if pfn is 0, we do a vm_insert_page (please see if (!page) line 1107) and folio handling in migrate_vma_finalize line 1284 Thanks, Balbir
