linux-kernel - [PATCH v3 19/19] mm, swap: remove no longer needed _swap_info

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Message-Id: <20251125-swap-table-p2-v3-19-33f54f707a5c@tencent.com>
Date: Tue, 25 Nov 2025 03:14:02 +0800
From: Kairui Song <ryncsn@...il.com>
To: linux-mm@...ck.org
Cc: Andrew Morton <akpm@...ux-foundation.org>, Baoquan He <bhe@...hat.com>, 
 Barry Song <baohua@...nel.org>, Chris Li <chrisl@...nel.org>, 
 Nhat Pham <nphamcs@...il.com>, Yosry Ahmed <yosry.ahmed@...ux.dev>, 
 David Hildenbrand <david@...nel.org>, Johannes Weiner <hannes@...xchg.org>, 
 Youngjun Park <youngjun.park@....com>, Hugh Dickins <hughd@...gle.com>, 
 Baolin Wang <baolin.wang@...ux.alibaba.com>, 
 Ying Huang <ying.huang@...ux.alibaba.com>, 
 Kemeng Shi <shikemeng@...weicloud.com>, 
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, 
 "Matthew Wilcox (Oracle)" <willy@...radead.org>, 
 linux-kernel@...r.kernel.org, Kairui Song <kasong@...cent.com>
Subject: [PATCH v3 19/19] mm, swap: remove no longer needed _swap_info_get

From: Kairui Song <kasong@...cent.com>

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@...cent.com>
---
 mm/swapfile.c | 47 ++++++-----------------------------------------
 1 file changed, 6 insertions(+), 41 deletions(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index eea904dc08d9..feb57e040ef1 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
@@ -1588,41 +1586,6 @@ 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)
@@ -1781,7 +1744,7 @@ 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;
 
@@ -1811,6 +1774,7 @@ int swp_swapcount(swp_entry_t entry)
 	} while (tmp_count & COUNT_CONTINUED);
 out:
 	swap_cluster_unlock(ci);
+	put_swap_device(si);
 	return count;
 }
 
@@ -1845,11 +1809,12 @@ 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, swp_offset(entry));
 

-- 
2.52.0