[PATCH v2 12/12] mm, swap: no need to clear the shadow explicitly

[Kairui Song <ryncsn@gmail.com>]

From: Kairui Song <kasong@tencent.com>

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.

Signed-off-by: Kairui Song <kasong@tencent.com>
---
 mm/swap.h       |  1 -
 mm/swap_state.c | 21 ---------------------
 mm/swapfile.c   |  2 --
 3 files changed, 24 deletions(-)

diff --git a/mm/swap.h b/mm/swap.h
index 3ee761ee8348..386a289ef8e7 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 c808f0948b10..20c4c2414db3 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 f5474ddbba36..d77c00c4b511 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

-- 
2.52.0