On 9/12/25 15:38, Mika Penttilä wrote: > > On 9/12/25 08:28, Mika Penttilä wrote: > >> On 9/12/25 08:04, Balbir Singh wrote: >> >>> 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 >> Ok actually seems it is handled by migrate_vma_insert_page() which does >> >> if (!pmd_none(*pmdp)) { >> if (pmd_trans_huge(*pmdp)) { >> if (!is_huge_zero_pmd(*pmdp)) >> goto abort; >> folio_get(pmd_folio(*pmdp)); >> split_huge_pmd(vma, pmdp, addr); <----- here >> } else if (pmd_leaf(*pmdp)) >> goto abort; >> } >> > While at it, think the folio_get(pmd_folio(*pmdp)); is wrong for here, > we split the pmd for huge zero page. >
Ack, will do Thanks for the review Balbir
