diff --git a/include/linux/mm.h b/include/linux/mm.h
index 6f4825d829656..795c89632265f 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2147,21 +2147,47 @@ static inline size_t folio_size(struct folio *folio)
 }
 
 /**
- * folio_estimated_sharers - Estimate the number of sharers of a folio.
+ * folio_likely_mapped_shared - Estimate if the folio is mapped into the page
+ *				tables of more than one MM
  * @folio: The folio.
  *
- * folio_estimated_sharers() aims to serve as a function to efficiently
- * estimate the number of processes sharing a folio. This is done by
- * looking at the precise mapcount of the first subpage in the folio, and
- * assuming the other subpages are the same. This may not be true for large
- * folios. If you want exact mapcounts for exact calculations, look at
- * page_mapcount() or folio_total_mapcount().
+ * This function checks if the folio is currently mapped into more than one
+ * MM ("mapped shared"), or if the folio is only mapped into a single MM
+ * ("mapped exclusively").
  *
- * Return: The estimated number of processes sharing a folio.
+ * As precise information is not easily available for all folios, this function
+ * estimates the number of MMs ("sharers") that are currently mapping a folio
+ * using the number of times the first page of the folio is currently mapped
+ * into page tables.
+ *
+ * For small anonymous folios (except KSM folios) and anonymous hugetlb folios,
+ * the return value will be exactly correct, because they can only be mapped
+ * at most once into an MM, and they cannot be partially mapped.
+ *
+ * For other folios, the result can be fuzzy:
+ * (a) For partially-mappable large folios (THP), the return value can wrongly
+ *     indicate "mapped exclusively" (false negative) when the folio is
+ *     only partially mapped into at least one MM.
+ * (b) For pagecache folios (including hugetlb), the return value can wrongly
+ *     indicate "mapped shared" (false positive) when two VMAs in the same MM
+ *     cover the same file range.
+ * (c) For (small) KSM folios, the return value can wrongly indicate "mapped
+ *     shared" (false negative), when the folio is mapped multiple times into
+ *     the same MM.
+ *
+ * Further, this function only considers current page table mappings that
+ * are tracked using the folio mapcount(s). It does not consider:
+ * (1) If the folio might get mapped in the (near) future (e.g., swapcache,
+ *     pagecache, temporary unmapping for migration).
+ * (2) If the folio is mapped differently (VM_PFNMAP).
+ * (3) If hugetlb page table sharing applies. Callers might want to check
+ *     hugetlb_pmd_shared().
+ *
+ * Return: Whether the folio is estimated to be mapped into more than one MM.
  */
-static inline int folio_estimated_sharers(struct folio *folio)
+static inline bool folio_likely_mapped_shared(struct folio *folio)
 {
-	return page_mapcount(folio_page(folio, 0));
+	return page_mapcount(folio_page(folio, 0)) > 1;
 }
 
 #ifndef HAVE_ARCH_MAKE_PAGE_ACCESSIBLE
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 50d146eb248ff..4d10904fef70c 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1829,7 +1829,7 @@ bool madvise_free_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
 	 * If other processes are mapping this folio, we couldn't discard
 	 * the folio unless they all do MADV_FREE so let's skip the folio.
 	 */
-	if (folio_estimated_sharers(folio) != 1)
+	if (folio_likely_mapped_shared(folio))
 		goto out;
 
 	if (!folio_trylock(folio))
diff --git a/mm/madvise.c b/mm/madvise.c
index 44a498c94158c..32a534d200219 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -366,7 +366,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
 		folio = pfn_folio(pmd_pfn(orig_pmd));
 
 		/* Do not interfere with other mappings of this folio */
-		if (folio_estimated_sharers(folio) != 1)
+		if (folio_likely_mapped_shared(folio))
 			goto huge_unlock;
 
 		if (pageout_anon_only_filter && !folio_test_anon(folio))
@@ -453,7 +453,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
 		if (folio_test_large(folio)) {
 			int err;
 
-			if (folio_estimated_sharers(folio) > 1)
+			if (folio_likely_mapped_shared(folio))
 				break;
 			if (pageout_anon_only_filter && !folio_test_anon(folio))
 				break;
@@ -677,7 +677,7 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
 		if (folio_test_large(folio)) {
 			int err;
 
-			if (folio_estimated_sharers(folio) != 1)
+			if (folio_likely_mapped_shared(folio))
 				break;
 			if (!folio_trylock(folio))
 				break;
diff --git a/mm/memory.c b/mm/memory.c
index 1c45b6a42a1b9..8394a9843ca06 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5173,7 +5173,7 @@ static vm_fault_t do_numa_page(struct vm_fault *vmf)
 	 * Flag if the folio is shared between multiple address spaces. This
 	 * is later used when determining whether to group tasks together
 	 */
-	if (folio_estimated_sharers(folio) > 1 && (vma->vm_flags & VM_SHARED))
+	if (folio_likely_mapped_shared(folio) && (vma->vm_flags & VM_SHARED))
 		flags |= TNF_SHARED;
 
 	nid = folio_nid(folio);
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index f60b4c99f1302..0b92fde395182 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -642,12 +642,11 @@ static int queue_folios_hugetlb(pte_t *pte, unsigned long hmask,
 	 * Unless MPOL_MF_MOVE_ALL, we try to avoid migrating a shared folio.
 	 * Choosing not to migrate a shared folio is not counted as a failure.
 	 *
-	 * To check if the folio is shared, ideally we want to make sure
-	 * every page is mapped to the same process. Doing that is very
-	 * expensive, so check the estimated sharers of the folio instead.
+	 * See folio_likely_mapped_shared() on possible imprecision when we
+	 * cannot easily detect if a folio is shared.
 	 */
 	if ((flags & MPOL_MF_MOVE_ALL) ||
-	    (folio_estimated_sharers(folio) == 1 && !hugetlb_pmd_shared(pte)))
+	    (!folio_likely_mapped_shared(folio) && !hugetlb_pmd_shared(pte)))
 		if (!isolate_hugetlb(folio, qp->pagelist))
 			qp->nr_failed++;
 unlock:
@@ -1032,11 +1031,10 @@ static bool migrate_folio_add(struct folio *folio, struct list_head *foliolist,
 	 * Unless MPOL_MF_MOVE_ALL, we try to avoid migrating a shared folio.
 	 * Choosing not to migrate a shared folio is not counted as a failure.
 	 *
-	 * To check if the folio is shared, ideally we want to make sure
-	 * every page is mapped to the same process. Doing that is very
-	 * expensive, so check the estimated sharers of the folio instead.
+	 * See folio_likely_mapped_shared() on possible imprecision when we
+	 * cannot easily detect if a folio is shared.
 	 */
-	if ((flags & MPOL_MF_MOVE_ALL) || folio_estimated_sharers(folio) == 1) {
+	if ((flags & MPOL_MF_MOVE_ALL) || !folio_likely_mapped_shared(folio)) {
 		if (folio_isolate_lru(folio)) {
 			list_add_tail(&folio->lru, foliolist);
 			node_stat_mod_folio(folio,
diff --git a/mm/migrate.c b/mm/migrate.c
index 73a052a382f13..35d376969f8b9 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2568,11 +2568,11 @@ int migrate_misplaced_folio(struct folio *folio, struct vm_area_struct *vma,
 	/*
 	 * Don't migrate file folios that are mapped in multiple processes
 	 * with execute permissions as they are probably shared libraries.
-	 * To check if the folio is shared, ideally we want to make sure
-	 * every page is mapped to the same process. Doing that is very
-	 * expensive, so check the estimated mapcount of the folio instead.
+	 *
+	 * See folio_likely_mapped_shared() on possible imprecision when we
+	 * cannot easily detect if a folio is shared.
 	 */
-	if (folio_estimated_sharers(folio) != 1 && folio_is_file_lru(folio) &&
+	if (folio_likely_mapped_shared(folio) && folio_is_file_lru(folio) &&
 	    (vma->vm_flags & VM_EXEC))
 		goto out;
 
