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 > for (addr = start; addr < end; addr += PAGE_SIZE) {
