[RFC PATCH 12/12] mm: provide is_swap_entry() and use it

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

Previously we have been in the insane situation where people check whether
we are in fact dealing with a swap entry by negating non_swap_entry() - so
determining if a swap entry is an entry for swap by checking that it's not
a not swap entry.

This is really rather sub-optimal, so rather than engaging in this dance,
and now we've eliminated confusing is_swap_pte() and is_swap_pmd() helpers,
and renamed non-swap entries to non-present entries, we are well placed to
introduce a new helper.

We therefore introduce is_swap_entry() for this purpose which simply
determines if a swp_entry_t value encodes an actual swap entry, and update
relevant callers to use this instead.

Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
---
 arch/s390/mm/gmap_helpers.c |  2 +-
 arch/s390/mm/pgtable.c      |  2 +-
 fs/proc/task_mmu.c          |  2 +-
 include/linux/swapops.h     | 15 +++++++++++++++
 mm/madvise.c                |  2 +-
 mm/memory.c                 |  4 ++--
 6 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/arch/s390/mm/gmap_helpers.c b/arch/s390/mm/gmap_helpers.c
index 2c41276a34c5..222a26d09cbb 100644
--- a/arch/s390/mm/gmap_helpers.c
+++ b/arch/s390/mm/gmap_helpers.c
@@ -28,7 +28,7 @@
  */
 static void ptep_zap_swap_entry(struct mm_struct *mm, swp_entry_t entry)
 {
-	if (!is_non_present_entry(entry))
+	if (is_swap_entry(entry))
 		dec_mm_counter(mm, MM_SWAPENTS);
 	else if (is_migration_entry(entry))
 		dec_mm_counter(mm, mm_counter(pfn_swap_entry_folio(entry)));
diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index 0c795f3c324f..a15befcf6a8c 100644
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -685,7 +685,7 @@ void ptep_unshadow_pte(struct mm_struct *mm, unsigned long saddr, pte_t *ptep)
 
 static void ptep_zap_swap_entry(struct mm_struct *mm, swp_entry_t entry)
 {
-	if (!is_non_present_entry(entry))
+	if (is_swap_entry(entry))
 		dec_mm_counter(mm, MM_SWAPENTS);
 	else if (is_migration_entry(entry)) {
 		struct folio *folio = pfn_swap_entry_folio(entry);
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 28f30e01e504..d62fdae57dce 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1022,7 +1022,7 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
 	} else {
 		swp_entry_t swpent = pte_to_swp_entry(ptent);
 
-		if (!is_non_present_entry(swpent)) {
+		if (is_swap_entry(swpent)) {
 			int mapcount;
 
 			mss->swap += PAGE_SIZE;
diff --git a/include/linux/swapops.h b/include/linux/swapops.h
index fb463d75fa90..c96c31671230 100644
--- a/include/linux/swapops.h
+++ b/include/linux/swapops.h
@@ -661,6 +661,21 @@ static inline bool is_non_present_entry(swp_entry_t entry)
 	return swp_type(entry) >= MAX_SWAPFILES;
 }
 
+/**
+ * is_swap_entry() - Determines if this is a swap entry.
+ * @entry: The entry to examine.
+ *
+ * Determines whether data encoded in non-present leaf page tables is a
+ * swap entry and NOT a migration entry, device private entry, market
+ * entry, etc.
+ *
+ * Returns true if it is a swap entry, otherwise false.
+ */
+static inline bool is_swap_entry(swp_entry_t entry)
+{
+	return !is_non_present_entry(entry);
+}
+
 static inline int is_pmd_non_present_folio_entry(pmd_t pmd)
 {
 	return is_pmd_migration_entry(pmd) || is_pmd_device_private_entry(pmd);
diff --git a/mm/madvise.c b/mm/madvise.c
index a259dae2b899..4bf098986cb4 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -690,7 +690,7 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
 			swp_entry_t entry;
 
 			entry = pte_to_swp_entry(ptent);
-			if (!is_non_present_entry(entry)) {
+			if (is_swap_entry(entry)) {
 				max_nr = (end - addr) / PAGE_SIZE;
 				nr = swap_pte_batch(pte, max_nr, ptent);
 				nr_swap -= nr;
diff --git a/mm/memory.c b/mm/memory.c
index 8968ba0b076f..4f4179eb70c0 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -931,7 +931,7 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 	struct page *page;
 	swp_entry_t entry = pte_to_swp_entry(orig_pte);
 
-	if (likely(!is_non_present_entry(entry))) {
+	if (likely(is_swap_entry(entry))) {
 		if (swap_duplicate(entry) < 0)
 			return -EIO;
 
@@ -1739,7 +1739,7 @@ static inline int zap_nonpresent_ptes(struct mmu_gather *tlb,
 		rss[mm_counter(folio)]--;
 		folio_remove_rmap_pte(folio, page, vma);
 		folio_put(folio);
-	} else if (!is_non_present_entry(entry)) {
+	} else if (is_swap_entry(entry)) {
 		/* Genuine swap entries, hence a private anon pages */
 		if (!should_zap_cows(details))
 			return 1;
-- 
2.51.0