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mm/huge_memory: adjust try_to_migrate_one() and split_huge_pmd_locked()

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Patch series "Clean up split_huge_pmd_locked() and remove unnecessary
folio pointers", v2.

The patch series enhances the folio verification by leveraging the
existing page_vma_mapped_walk() mechanism and removing redundant folio
pointer passing.


This patch (of 2):

split_huge_pmd_locked() currently performs redundant checks for migration
entries and folio validation that are already handled by the
page_vma_mapped_walk mechanism in try_to_migrate_one.

Specifically, page_vma_mapped_walk already ensures that:
- The folio is properly mapped in the given VMA area
- pmd_trans_huge, pmd_devmap, and migration entry validation are
  performed

To leverage page_vma_mapped_walk's work, moving TTU_SPLIT_HUGE_PMD
handling to the while loop checking and removing these duplicate checks
from split_huge_pmd_locked.

Link: https://lkml.kernel.org/r/20250425103859.825879-1-gavinguo@igalia.com
Link: https://lkml.kernel.org/r/20250425103859.825879-2-gavinguo@igalia.com
Link: https://lore.kernel.org/all/98d1d195-7821-4627-b518-83103ade56c0@redhat.com/
Link: https://lore.kernel.org/all/91599a3c-e69e-4d79-bac5-5013c96203d7@redhat.com/
Signed-off-by: Gavin Guo <gavinguo@igalia.com>
Suggested-by: David Hildenbrand <david@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Florent Revest <revest@google.com>
Cc: Gavin Shan <gshan@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Gavin Guo 2025-04-25 18:38:58 +08:00 • committed by Andrew Morton
parent 7d709f49ba
commit 60fbb14396
2 changed files with 11 additions and 28 deletions
Download patch file Download diff file Expand all files Collapse all files

21
mm/huge_memory.c
View file

@ -3082,27 +3082,10 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
void split_huge_pmd_locked(struct vm_area_struct *vma, unsigned long address,
pmd_t *pmd, bool freeze, struct folio *folio)
{
bool pmd_migration = is_pmd_migration_entry(*pmd);
VM_WARN_ON_ONCE(folio && !folio_test_pmd_mappable(folio));
VM_WARN_ON_ONCE(!IS_ALIGNED(address, HPAGE_PMD_SIZE));
VM_WARN_ON_ONCE(folio && !folio_test_locked(folio));
VM_BUG_ON(freeze && !folio);
/*
* When the caller requests to set up a migration entry, we
* require a folio to check the PMD against. Otherwise, there
* is a risk of replacing the wrong folio.
*/
if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd) || pmd_migration) {
/*
* Do not apply pmd_folio() to a migration entry; and folio lock
* guarantees that it must be of the wrong folio anyway.
*/
if (folio && (pmd_migration || folio != pmd_folio(*pmd)))
return;
if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd) ||
is_pmd_migration_entry(*pmd))
__split_huge_pmd_locked(vma, pmd, address, freeze);
}
}
void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,

18
mm/rmap.c
View file

@ -2291,13 +2291,6 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
if (flags & TTU_SYNC)
pvmw.flags = PVMW_SYNC;
/*
* unmap_page() in mm/huge_memory.c is the only user of migration with
* TTU_SPLIT_HUGE_PMD and it wants to freeze.
*/
if (flags & TTU_SPLIT_HUGE_PMD)
split_huge_pmd_address(vma, address, true, folio);
/*
* For THP, we have to assume the worse case ie pmd for invalidation.
* For hugetlb, it could be much worse if we need to do pud
@ -2323,9 +2316,16 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
mmu_notifier_invalidate_range_start(&range);
while (page_vma_mapped_walk(&pvmw)) {
#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
/* PMD-mapped THP migration entry */
if (!pvmw.pte) {
if (flags & TTU_SPLIT_HUGE_PMD) {
split_huge_pmd_locked(vma, pvmw.address,
pvmw.pmd, true, NULL);
ret = false;
page_vma_mapped_walk_done(&pvmw);
break;
}
#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
subpage = folio_page(folio,
pmd_pfn(*pvmw.pmd) - folio_pfn(folio));
VM_BUG_ON_FOLIO(folio_test_hugetlb(folio) ||
@ -2337,8 +2337,8 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
break;
}
continue;
}
#endif
}
/* Unexpected PMD-mapped THP? */
VM_BUG_ON_FOLIO(!pvmw.pte, folio);