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mm/migrate_device: handle partially mapped folios during collection

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Extend migrate_vma_collect_pmd() to handle partially mapped large folios
that require splitting before migration can proceed.

During PTE walk in the collection phase, if a large folio is only
partially mapped in the migration range, it must be split to ensure the
folio is correctly migrated.

[matthew.brost@intel.com: handle partially mapped folios during split]
  Link: https://lkml.kernel.org/r/20251120230825.181072-1-matthew.brost@intel.com
Link: https://lkml.kernel.org/r/20251001065707.920170-7-balbirs@nvidia.com
Signed-off-by: Balbir Singh <balbirs@nvidia.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: Ying Huang <ying.huang@linux.alibaba.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: "Liam R. Howlett" <Liam.Howlett@oracle.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Lyude Paul <lyude@redhat.com>
Cc: Danilo Krummrich <dakr@kernel.org>
Cc: David Airlie <airlied@gmail.com>
Cc: Simona Vetter <simona@ffwll.ch>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Mika Penttilä <mpenttil@redhat.com>
Cc: Francois Dugast <francois.dugast@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Balbir Singh 2025-10-01 16:56:57 +10:00 • committed by Andrew Morton
parent 1462872900
commit 022a12deda
1 changed files with 69 additions and 1 deletions
Download patch file Download diff file Expand all files Collapse all files

70
mm/migrate_device.c
View file

@ -54,6 +54,55 @@ static int migrate_vma_collect_hole(unsigned long start,
return 0;
}
/**
* migrate_vma_split_folio() - Helper function to split a THP folio
* @folio: the folio to split
* @fault_page: struct page associated with the fault if any
*
* Returns 0 on success
*/
static int migrate_vma_split_folio(struct folio *folio,
struct page *fault_page)
{
int ret;
struct folio *fault_folio = fault_page ? page_folio(fault_page) : NULL;
struct folio *new_fault_folio = NULL;
if (folio != fault_folio) {
folio_get(folio);
folio_lock(folio);
}
ret = split_folio(folio);
if (ret) {
if (folio != fault_folio) {
folio_unlock(folio);
folio_put(folio);
}
return ret;
}
new_fault_folio = fault_page ? page_folio(fault_page) : NULL;
/*
* Ensure the lock is held on the correct
* folio after the split
*/
if (!new_fault_folio) {
folio_unlock(folio);
folio_put(folio);
} else if (folio != new_fault_folio) {
if (new_fault_folio != fault_folio) {
folio_get(new_fault_folio);
folio_lock(new_fault_folio);
}
folio_unlock(folio);
folio_put(folio);
}
return 0;
}
static int migrate_vma_collect_pmd(pmd_t *pmdp,
unsigned long start,
unsigned long end,
@ -107,10 +156,11 @@ again:
}
}
ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl);
ptep = pte_offset_map_lock(mm, pmdp, start, &ptl);
if (!ptep)
goto again;
arch_enter_lazy_mmu_mode();
ptep += (addr - start) / PAGE_SIZE;
for (; addr < end; addr += PAGE_SIZE, ptep++) {
struct dev_pagemap *pgmap;
@ -171,6 +221,24 @@ again:
pgmap->owner != migrate->pgmap_owner)
goto next;
}
folio = page ? page_folio(page) : NULL;
if (folio && folio_test_large(folio)) {
int ret;
arch_leave_lazy_mmu_mode();
pte_unmap_unlock(ptep, ptl);
ret = migrate_vma_split_folio(folio,
migrate->fault_page);
if (ret) {
if (unmapped)
flush_tlb_range(walk->vma, start, end);
return migrate_vma_collect_skip(addr, end, walk);
}
goto again;
}
mpfn = migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE;
mpfn |= pte_write(pte) ? MIGRATE_PFN_WRITE : 0;
}