From: Kairui Song <kasong@tencent.com>
Date: Tue, 17 Feb 2026 20:06:37 +0000 (+0800)
Subject: mm, swap: no need to clear the shadow explicitly
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=1df1a1b950863e64c00d48df718ed7ed28db3ea3;p=thirdparty%2Fkernel%2Flinux.git

mm, swap: no need to clear the shadow explicitly

Since we no longer bypass the swap cache, every swap-in will clear the
swap shadow by inserting the folio into the swap table.  The only place we
may seem to need to free the swap shadow is when the swap slots are freed
directly without a folio (swap_put_entries_direct).  But with the swap
table, that is not needed either.  Freeing a slot in the swap table will
set the table entry to NULL, which erases the shadow just fine.

So just delete all explicit shadow clearing, it's no longer needed.  Also,
rearrange the freeing.

Link: https://lkml.kernel.org/r/20260218-swap-table-p3-v3-12-f4e34be021a7@tencent.com
Signed-off-by: Kairui Song <kasong@tencent.com>
Acked-by: Chris Li <chrisl@kernel.org>
Cc: Baoquan He <bhe@redhat.com>
Cc: Barry Song <baohua@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kairui Song <ryncsn@gmail.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: kernel test robot <lkp@intel.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

diff --git a/mm/swap.h b/mm/swap.h
index 9728e6a944b2f..a77016f2423b9 100644
--- a/mm/swap.h
+++ b/mm/swap.h
@@ -290,7 +290,6 @@ void __swap_cache_del_folio(struct swap_cluster_info *ci,
 			    struct folio *folio, swp_entry_t entry, void *shadow);
 void __swap_cache_replace_folio(struct swap_cluster_info *ci,
 				struct folio *old, struct folio *new);
-void __swap_cache_clear_shadow(swp_entry_t entry, int nr_ents);
 
 void show_swap_cache_info(void);
 void swapcache_clear(struct swap_info_struct *si, swp_entry_t entry, int nr);
diff --git a/mm/swap_state.c b/mm/swap_state.c
index e7618ffe6d708..32d9d877bda8d 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -350,27 +350,6 @@ void __swap_cache_replace_folio(struct swap_cluster_info *ci,
 	}
 }
 
-/**
- * __swap_cache_clear_shadow - Clears a set of shadows in the swap cache.
- * @entry: The starting index entry.
- * @nr_ents: How many slots need to be cleared.
- *
- * Context: Caller must ensure the range is valid, all in one single cluster,
- * not occupied by any folio, and lock the cluster.
- */
-void __swap_cache_clear_shadow(swp_entry_t entry, int nr_ents)
-{
-	struct swap_cluster_info *ci = __swap_entry_to_cluster(entry);
-	unsigned int ci_off = swp_cluster_offset(entry), ci_end;
-	unsigned long old;
-
-	ci_end = ci_off + nr_ents;
-	do {
-		old = __swap_table_xchg(ci, ci_off, null_to_swp_tb());
-		WARN_ON_ONCE(swp_tb_is_folio(old) || swp_tb_get_count(old));
-	} while (++ci_off < ci_end);
-}
-
 /*
  * If we are the only user, then try to free up the swap cache.
  *
diff --git a/mm/swapfile.c b/mm/swapfile.c
index f9ba89cb290c2..915bc93964dbd 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1287,7 +1287,6 @@ static void swap_range_alloc(struct swap_info_struct *si,
 static void swap_range_free(struct swap_info_struct *si, unsigned long offset,
 			    unsigned int nr_entries)
 {
-	unsigned long begin = offset;
 	unsigned long end = offset + nr_entries - 1;
 	void (*swap_slot_free_notify)(struct block_device *, unsigned long);
 	unsigned int i;
@@ -1312,7 +1311,6 @@ static void swap_range_free(struct swap_info_struct *si, unsigned long offset,
 			swap_slot_free_notify(si->bdev, offset);
 		offset++;
 	}
-	__swap_cache_clear_shadow(swp_entry(si->type, begin), nr_entries);
 
 	/*
 	 * Make sure that try_to_unuse() observes si->inuse_pages reaching 0