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

Lorenzo Stoakes
2025-10-24T07:43:26Z

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