[PATCH v2 6/9] mm/swapfile: Add batched version of folio_dup_swap

Dev Jain
2026-04-10T10:33:13Z

Add folio_dup_swap_pages to handle a batch of consecutive pages. Note
that folio_dup_swap already can handle a subset of this: nr_pages == 1 and
nr_pages == folio_nr_pages(folio). Generalize this to any nr_pages.

Currently we have a not-so-nice logic of passing in subpage == NULL if
we mean to exercise the logic on the entire folio, and subpage != NULL if
we want to exercise the logic on only that subpage. Remove this
indirection: the caller invokes folio_dup_swap_pages() if it wants to
operate on a range of pages in the folio (i.e nr_pages may be anything
between 1 till folio_nr_pages()), and invokes folio_dup_swap() if it
wants to operate on the entire folio.

Signed-off-by: Dev Jain <dev.jain@arm.com>
---
mm/rmap.c | 2 +-
mm/shmem.c | 2 +-
mm/swap.h | 12 ++++++++++--
mm/swapfile.c | 20 ++++++++++++--------
4 files changed, 24 insertions(+), 12 deletions(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index 7a150edd96819..6412103fcd6cb 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -2311,7 +2311,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
goto finish_unmap;
}

- if (folio_dup_swap(folio, subpage) < 0) {
+ if (folio_dup_swap_pages(folio, subpage, 1) < 0) {
set_pte_at(mm, address, pvmw.pte, pteval);
goto walk_abort;
}
diff --git a/mm/shmem.c b/mm/shmem.c
index 5aa43657886c3..3f9523c97b9ed 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1695,7 +1695,7 @@ int shmem_writeout(struct folio *folio, struct swap_iocb **plug,
spin_unlock(&shmem_swaplist_lock);
}

- folio_dup_swap(folio, NULL);
+ folio_dup_swap(folio);
shmem_delete_from_page_cache(folio, swp_to_radix_entry(folio->swap));

BUG_ON(folio_mapped(folio));
diff --git a/mm/swap.h b/mm/swap.h
index a77016f2423b9..3c25f914e908b 100644
--- a/mm/swap.h
+++ b/mm/swap.h
@@ -206,7 +206,9 @@ extern int swap_retry_table_alloc(swp_entry_t entry, gfp_t gfp);
* folio_put_swap(): does the opposite thing of folio_dup_swap().
*/
int folio_alloc_swap(struct folio *folio);
-int folio_dup_swap(struct folio *folio, struct page *subpage);
+int folio_dup_swap(struct folio *folio);
+int folio_dup_swap_pages(struct folio *folio, struct page *page,
+ unsigned long nr_pages);
void folio_put_swap(struct folio *folio, struct page *subpage);

/* For internal use */
@@ -390,7 +392,13 @@ static inline int folio_alloc_swap(struct folio *folio)
return -EINVAL;
}

-static inline int folio_dup_swap(struct folio *folio, struct page *page)
+static inline int folio_dup_swap(struct folio *folio)
+{
+ return -EINVAL;
+}
+
+static inline int folio_dup_swap_pages(struct folio *folio, struct page *page,
+ unsigned long nr_pages)
{
return -EINVAL;
}
diff --git a/mm/swapfile.c b/mm/swapfile.c
index ff315b752afd3..22be05a0bb200 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1740,9 +1740,10 @@ int folio_alloc_swap(struct folio *folio)
}

/**
- * folio_dup_swap() - Increase swap count of swap entries of a folio.
+ * folio_dup_swap_pages() - Increase swap count of swap entries of a folio.
* @folio: folio with swap entries bounded.
- * @subpage: if not NULL, only increase the swap count of this subpage.
+ * @page: the first page in the folio to increase the swap count for.
+ * @nr_pages: the number of pages in the folio to increase the swap count for.
*
* Typically called when the folio is unmapped and have its swap entry to
* take its place: Swap entries allocated to a folio has count == 0 and pinned
@@ -1756,23 +1757,26 @@ int folio_alloc_swap(struct folio *folio)
* swap_put_entries_direct on its swap entry before this helper returns, or
* the swap count may underflow.
*/
-int folio_dup_swap(struct folio *folio, struct page *subpage)
+int folio_dup_swap_pages(struct folio *folio, struct page *page,
+ unsigned long nr_pages)
{
swp_entry_t entry = folio->swap;
- unsigned long nr_pages = folio_nr_pages(folio);

VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio);
VM_WARN_ON_FOLIO(!folio_test_swapcache(folio), folio);

- if (subpage) {
- entry.val += folio_page_idx(folio, subpage);
- nr_pages = 1;
- }
+ entry.val += folio_page_idx(folio, page);

return swap_dup_entries_cluster(swap_entry_to_info(entry),
swp_offset(entry), nr_pages);
}

+int folio_dup_swap(struct folio *folio)
+{
+ return folio_dup_swap_pages(folio, folio_page(folio, 0),
+ folio_nr_pages(folio));
+}
+
/**
* folio_put_swap() - Decrease swap count of swap entries of a folio.
* @folio: folio with swap entries bounded, must be in swap cache and locked.
--
2.34.1