Commit 60fbb143 authored by Gavin Guo's avatar Gavin Guo Committed by Andrew Morton
Browse files

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

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: default avatarGavin Guo <gavinguo@igalia.com>
Suggested-by: default avatarDavid Hildenbrand <david@redhat.com>
Acked-by: default avatarDavid Hildenbrand <david@redhat.com>
Reviewed-by: default avatarZi Yan <ziy@nvidia.com>
Reviewed-by: default avatarBaolin 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: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 7d709f49

mm/huge_memory.c

+2 −19
Original line number Diff line number Diff line
@@ -3082,28 +3082,11 @@ 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,

		unsigned long address, bool freeze, struct folio *folio)

mm/rmap.c

+9 −9
Original line number Diff line number Diff line
@@ -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);