[PATCH v5 19/19] mm, swap: remove no longer needed _swap_info_get

Kairui Song
2025-12-19T19:45:49Z

There are now only two users of _swap_info_get after consolidating
these callers, folio_free_swap and swp_swapcount.

folio_free_swap already holds the folio lock, and the folio
must be in the swap cache, _swap_info_get is redundant.

For swp_swapcount, it should use get_swap_device instead. get_swap_device
increases the device ref count, which is actually a bit safer. The
only current use is smap walking, and the performance change here
is tiny.

And after these changes, _swap_info_get is no longer used, so we can
safely remove it.

Signed-off-by: Kairui Song <kasong@tencent.com>
---
mm/swapfile.c | 47 ++++++-----------------------------------------
1 file changed, 6 insertions(+), 41 deletions(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 886f9d6d1a2c..1ee13390d910 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -83,9 +83,7 @@ bool swap_migration_ad_supported;
#endif /* CONFIG_MIGRATION */

static const char Bad_file[] = "Bad swap file entry ";
-static const char Unused_file[] = "Unused swap file entry ";
static const char Bad_offset[] = "Bad swap offset entry ";
-static const char Unused_offset[] = "Unused swap offset entry ";

/*
* all active swap_info_structs
@@ -1600,41 +1598,6 @@ void folio_put_swap(struct folio *folio, struct page *subpage)
swap_put_entries_cluster(si, swp_offset(entry), nr_pages, false);
}

-static struct swap_info_struct *_swap_info_get(swp_entry_t entry)
-{
- struct swap_info_struct *si;
- unsigned long offset;
-
- if (!entry.val)
- goto out;
- si = swap_entry_to_info(entry);
- if (!si)
- goto bad_nofile;
- if (data_race(!(si->flags & SWP_USED)))
- goto bad_device;
- offset = swp_offset(entry);
- if (offset >= si->max)
- goto bad_offset;
- if (data_race(!si->swap_map[swp_offset(entry)]) &&
- !swap_cache_has_folio(entry))
- goto bad_free;
- return si;
-
-bad_free:
- pr_err("%s: %s%08lx\n", __func__, Unused_offset, entry.val);
- goto out;
-bad_offset:
- pr_err("%s: %s%08lx\n", __func__, Bad_offset, entry.val);
- goto out;
-bad_device:
- pr_err("%s: %s%08lx\n", __func__, Unused_file, entry.val);
- goto out;
-bad_nofile:
- pr_err("%s: %s%08lx\n", __func__, Bad_file, entry.val);
-out:
- return NULL;
-}
-
static void swap_put_entry_locked(struct swap_info_struct *si,
struct swap_cluster_info *ci,
unsigned long offset)
@@ -1794,7 +1757,7 @@ int swp_swapcount(swp_entry_t entry)
pgoff_t offset;
unsigned char *map;

- si = _swap_info_get(entry);
+ si = get_swap_device(entry);
if (!si)
return 0;

@@ -1824,6 +1787,7 @@ int swp_swapcount(swp_entry_t entry)
} while (tmp_count & COUNT_CONTINUED);
out:
swap_cluster_unlock(ci);
+ put_swap_device(si);
return count;
}

@@ -1858,11 +1822,12 @@ static bool swap_page_trans_huge_swapped(struct swap_info_struct *si,
static bool folio_swapped(struct folio *folio)
{
swp_entry_t entry = folio->swap;
- struct swap_info_struct *si = _swap_info_get(entry);
+ struct swap_info_struct *si;

- if (!si)
- return false;
+ VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio);
+ VM_WARN_ON_ONCE_FOLIO(!folio_test_swapcache(folio), folio);

+ si = __swap_entry_to_info(entry);
if (!IS_ENABLED(CONFIG_THP_SWAP) || likely(!folio_test_large(folio)))
return swap_entry_swapped(si, entry);

--
2.52.0