mm/zswap: remove SWP_SYNCHRONOUS_IO swapcache bypass workaround

Since commit f1879e8a0c60 ("mm, swap: never bypass the swap cache even for
SWP_SYNCHRONOUS_IO"), all swap-in operations go through the swap cache,
including those from SWP_SYNCHRONOUS_IO devices like zram.  Which means
the workaround for swap cache bypassing introduced by commit 25cd241408a2
("mm: zswap: fix data loss on SWP_SYNCHRONOUS_IO devices") is no longer
needed.  Remove it, but keep the comments that are still helpful.

Link: https://lkml.kernel.org/r/20260202-zswap-syncio-cleanup-v1-1-86bb24a64521@tencent.com
Signed-off-by: Kairui Song <kasong@tencent.com>
Suggested-by: Yosry Ahmed <yosry.ahmed@linux.dev>
Reviewed-by: Barry Song <baohua@kernel.org>
Acked-by: Chris Li <chrisl@kernel.org>
Acked-by: Yosry Ahmed <yosry.ahmed@linux.dev>
Acked-by: Nhat Pham <nphamcs@gmail.com>
Reviewed-by: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Baoquan He <bhe@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kairui Song <kasong@tencent.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 6 insertions, 13 deletions

diff --git a/mm/zswap.c b/mm/zswap.c
index 16b2ef7223e1..0823cadd02b6 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -1595,11 +1595,11 @@ int zswap_load(struct folio *folio)
 {
 	swp_entry_t swp = folio->swap;
 	pgoff_t offset = swp_offset(swp);
-	bool swapcache = folio_test_swapcache(folio);
 	struct xarray *tree = swap_zswap_tree(swp);
 	struct zswap_entry *entry;
 
 	VM_WARN_ON_ONCE(!folio_test_locked(folio));
+	VM_WARN_ON_ONCE(!folio_test_swapcache(folio));
 
 	if (zswap_never_enabled())
 		return -ENOENT;
@@ -1630,22 +1630,15 @@ int zswap_load(struct folio *folio)
 		count_objcg_events(entry->objcg, ZSWPIN, 1);
 
 	/*
-	 * When reading into the swapcache, invalidate our entry. The
-	 * swapcache can be the authoritative owner of the page and
+	 * We are reading into the swapcache, invalidate zswap entry.
+	 * The swapcache is the authoritative owner of the page and
 	 * its mappings, and the pressure that results from having two
 	 * in-memory copies outweighs any benefits of caching the
 	 * compression work.
-	 *
-	 * (Most swapins go through the swapcache. The notable
-	 * exception is the singleton fault on SWP_SYNCHRONOUS_IO
-	 * files, which reads into a private page and may free it if
-	 * the fault fails. We remain the primary owner of the entry.)
 	 */
-	if (swapcache) {
-		folio_mark_dirty(folio);
-		xa_erase(tree, offset);
-		zswap_entry_free(entry);
-	}
+	folio_mark_dirty(folio);
+	xa_erase(tree, offset);
+	zswap_entry_free(entry);
 
 	folio_unlock(folio);
 	return 0;