protection(struct mmu_gather *tlb, struct vm_area_struct *vm
  	hugetlb_vma_unlock_write(vma);
  	mmu_notifier_invalidate_range_end(&range);
  
+	tlb_end_vma(tlb, vma);
+
  	return pages > 0 ? (pages << h->order) : pages;
  }
  
@@ -7259,6 +7266,9 @@ static void hugetlb_unshare_pmds(struct vm_area_struct *vma,
  	} else {
  		i_mmap_assert_write_locked(vma->vm_file->f_mapping);
  	}
+
+	tlb_change_page_size(&tlb, sz);
+	tlb_start_vma(&tlb, vma);
  	for (address = start; address < end; address += PUD_SIZE) {
  		ptep = hugetlb_walk(vma, address, sz);
  		if (!ptep)
diff --git a/mm/rmap.c b/mm/rmap.c
index d6799afe11147..27210bc6fb489 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -2015,6 +2015,8 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
  					goto walk_abort;
  
  				tlb_gather_mmu(&tlb, mm);
+				tlb_change_page_size(&tlb, huge_page_size(hstate_vma(vma)));
+				tlb_start_vma(&tlb, vma);
  				if (huge_pmd_unshare(&tlb, vma, address, pvmw.pte)) {
  					hugetlb_vma_unlock_write(vma);
  					huge_pmd_unshare_flush(&tlb, vma);
@@ -2413,6 +2415,8 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
  				}
  
  				tlb_gather_mmu(&tlb, mm);
+				tlb_change_page_size(&tlb, huge_page_size(hstate_vma(vma)));
+				tlb_start_vma(&tlb, vma);
  				if (huge_pmd_unshare(&tlb, vma, address, pvmw.pte)) {
  					hugetlb_vma_unlock_write(vma);
  					huge_pmd_unshare_flush(&tlb, vma);
-- 
2.52.0



But now I'm staring at it and wonder whether we should just defer the TLB flushing changes
to a later point and only focus on the IPI flushes. Doing only that with mmu_gather
looks *really* weird, and I don't want to introduce some other mechanism just for that
batching purpose.

Hm ...

-- 
Cheers

David[PATCH v2 4/4] mm/hugetlb: fix excessive IPI broadcasts when unsharing PMD tables using mmu_gather"David Hildenbrand (Red Hat)" <david@kernel.org> undefinedHarry Yoo <harry.yoo@oracle.com> undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined™