mm/rmap: integrate PMD-mapped folio splitting into pagewalk loop

In preparation for supporting try_to_unmap_one() to unmap PMD-mapped
folios, start the pagewalk first, then call split_huge_pmd_address() to
split the folio.

Link: https://lkml.kernel.org/r/20240614015138.31461-3-ioworker0@gmail.com
Signed-off-by: Lance Yang <ioworker0@gmail.com>
Suggested-by: David Hildenbrand <david@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Suggested-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Acked-by: Zi Yan <ziy@nvidia.com>
Cc: Bang Li <libang.li@antgroup.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Fangrui Song <maskray@google.com>
Cc: Jeff Xie <xiehuan09@gmail.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Yin Fengwei <fengwei.yin@intel.com>
Cc: Zach O'Keefe <zokeefe@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 22 insertions, 20 deletions

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 6b294c9160de1..b247490a09312 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2583,6 +2583,27 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
 	pmd_populate(mm, pmd, pgtable);
 }
 
+void split_huge_pmd_locked(struct vm_area_struct *vma, unsigned long address,
+			   pmd_t *pmd, bool freeze, struct folio *folio)
+{
+	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) ||
+	    is_pmd_migration_entry(*pmd)) {
+		if (folio && folio != pmd_folio(*pmd))
+			return;
+		__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)
 {
@@ -2594,26 +2615,7 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
 				(address & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE);
 	mmu_notifier_invalidate_range_start(&range);
 	ptl = pmd_lock(vma->vm_mm, pmd);
-
-	/*
-	 * If caller asks to setup a migration entry, we need a folio to check
-	 * pmd against. Otherwise we can end up replacing wrong folio.
-	 */
-	VM_BUG_ON(freeze && !folio);
-	VM_WARN_ON_ONCE(folio && !folio_test_locked(folio));
-
-	if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd) ||
-	    is_pmd_migration_entry(*pmd)) {
-		/*
-		 * It's safe to call pmd_page when folio is set because it's
-		 * guaranteed that pmd is present.
-		 */
-		if (folio && folio != pmd_folio(*pmd))
-			goto out;
-		__split_huge_pmd_locked(vma, pmd, range.start, freeze);
-	}
-
-out:
+	split_huge_pmd_locked(vma, range.start, pmd, freeze, folio);
 	spin_unlock(ptl);
 	mmu_notifier_invalidate_range_end(&range);
 }