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. >> Thanks, >> Balbir >> > --Mika >
