[PATCH v3 7/9] mm/swapfile: Add batched version of folio_put_swap

Dev Jain
2026-05-06T09:46:19Z

Add folio_put_swap_pages to handle a batch of consecutive pages. Note
that folio_put_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_put_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_put_swap() if it
wants to operate on the entire folio.

Signed-off-by: Dev Jain <dev.jain@arm.com>
---
mm/memory.c | 6 +++---
mm/rmap.c | 4 ++--
mm/shmem.c | 6 +++---
mm/swap.h | 11 +++++++++--
mm/swapfile.c | 22 +++++++++++++---------
5 files changed, 30 insertions(+), 19 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index f14311c4d2001..c5605a779ce4d 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5104,7 +5104,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
if (unlikely(folio != swapcache)) {
folio_add_new_anon_rmap(folio, vma, address, RMAP_EXCLUSIVE);
folio_add_lru_vma(folio, vma);
- folio_put_swap(swapcache, NULL);
+ folio_put_swap(swapcache);
} else if (!folio_test_anon(folio)) {
/*
* We currently only expect !anon folios that are fully
@@ -5113,12 +5113,12 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
VM_WARN_ON_ONCE_FOLIO(folio_nr_pages(folio) != nr_pages, folio);
VM_WARN_ON_ONCE_FOLIO(folio_mapped(folio), folio);
folio_add_new_anon_rmap(folio, vma, address, rmap_flags);
- folio_put_swap(folio, NULL);
+ folio_put_swap(folio);
} else {
VM_WARN_ON_ONCE(nr_pages != 1 && nr_pages != folio_nr_pages(folio));
folio_add_anon_rmap_ptes(folio, page, nr_pages, vma, address,
rmap_flags);
- folio_put_swap(folio, nr_pages == 1 ? page : NULL);
+ folio_put_swap_pages(folio, page, nr_pages);
}

VM_BUG_ON(!folio_test_anon(folio) ||
diff --git a/mm/rmap.c b/mm/rmap.c
index 352ba77d90f67..7cbf850182187 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -2325,7 +2325,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
* so we'll not check/care.
*/
if (arch_unmap_one(mm, vma, address, pteval) < 0) {
- folio_put_swap(folio, subpage);
+ folio_put_swap_pages(folio, subpage, 1);
set_pte_at(mm, address, pvmw.pte, pteval);
goto walk_abort;
}
@@ -2333,7 +2333,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
/* See folio_try_share_anon_rmap(): clear PTE first. */
if (anon_exclusive &&
folio_try_share_anon_rmap_pte(folio, subpage)) {
- folio_put_swap(folio, subpage);
+ folio_put_swap_pages(folio, subpage, 1);
set_pte_at(mm, address, pvmw.pte, pteval);
goto walk_abort;
}
diff --git a/mm/shmem.c b/mm/shmem.c
index 5e4f521399847..bb7e0fc305d87 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1719,7 +1719,7 @@ int shmem_writeout(struct folio *folio, struct swap_iocb **plug,
/* Swap entry might be erased by racing shmem_free_swap() */
if (!error) {
shmem_recalc_inode(inode, 0, -nr_pages);
- folio_put_swap(folio, NULL);
+ folio_put_swap(folio);
}

/*
@@ -2199,7 +2199,7 @@ static void shmem_set_folio_swapin_error(struct inode *inode, pgoff_t index,

nr_pages = folio_nr_pages(folio);
folio_wait_writeback(folio);
- folio_put_swap(folio, NULL);
+ folio_put_swap(folio);
swap_cache_del_folio(folio);
/*
* Don't treat swapin error folio as alloced. Otherwise inode->i_blocks
@@ -2429,7 +2429,7 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
if (sgp == SGP_WRITE)
folio_mark_accessed(folio);

- folio_put_swap(folio, NULL);
+ folio_put_swap(folio);
swap_cache_del_folio(folio);
folio_mark_dirty(folio);
put_swap_device(si);
diff --git a/mm/swap.h b/mm/swap.h
index 3c25f914e908b..343547469927a 100644
--- a/mm/swap.h
+++ b/mm/swap.h
@@ -209,7 +209,9 @@ int folio_alloc_swap(struct folio *folio);
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);
+void folio_put_swap(struct folio *folio);
+void folio_put_swap_pages(struct folio *folio, struct page *page,
+ unsigned long nr_pages);

/* For internal use */
extern void __swap_cluster_free_entries(struct swap_info_struct *si,
@@ -403,7 +405,12 @@ static inline int folio_dup_swap_pages(struct folio *folio, struct page *page,
return -EINVAL;
}

-static inline void folio_put_swap(struct folio *folio, struct page *page)
+static inline void folio_put_swap(struct folio *folio)
+{
+}
+
+static inline void folio_put_swap_pages(struct folio *folio, struct page *page,
+ unsigned long nr_pages)
{
}

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 28daf92839e77..ac576cc63b194 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1778,31 +1778,34 @@ int folio_dup_swap(struct folio *folio)
}

/**
- * folio_put_swap() - Decrease swap count of swap entries of a folio.
+ * folio_put_swap_pages() - Decrease swap count of swap entries of a folio.
* @folio: folio with swap entries bounded, must be in swap cache and locked.
- * @subpage: if not NULL, only decrease the swap count of this subpage.
+ * @page: the first page in the folio to decrease the swap count for.
+ * @nr_pages: the number of pages in the folio to decrease the swap count for.
*
* This won't free the swap slots even if swap count drops to zero, they are
* still pinned by the swap cache. User may call folio_free_swap to free them.
* Context: Caller must ensure the folio is locked and in the swap cache.
*/
-void folio_put_swap(struct folio *folio, struct page *subpage)
+void folio_put_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);
struct swap_info_struct *si = __swap_entry_to_info(entry);

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);

swap_put_entries_cluster(si, swp_offset(entry), nr_pages, false);
}

+void folio_put_swap(struct folio *folio)
+{
+ folio_put_swap_pages(folio, folio_page(folio, 0), folio_nr_pages(folio));
+}
+
/*
* When we get a swap entry, if there aren't some other ways to
* prevent swapoff, such as the folio in swap cache is locked, RCU
@@ -2443,7 +2446,8 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
new_pte = pte_mkuffd_wp(new_pte);
setpte:
set_pte_at(vma->vm_mm, addr, pte, new_pte);
- folio_put_swap(swapcache, folio_file_page(swapcache, swp_offset(entry)));
+ folio_put_swap_pages(swapcache,
+ folio_file_page(swapcache, swp_offset(entry)), 1);
out:
if (pte)
pte_unmap_unlock(pte, ptl);
--
2.34.1