linux-kernel - [PATCH 4/6] mm/zswap: remove duplicate

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Message-Id: <20240201-b4-zswap-invalidate-entry-v1-4-56ed496b6e55@bytedance.com>
Date: Thu, 01 Feb 2024 15:49:04 +0000
From: Chengming Zhou <zhouchengming@...edance.com>
To: Nhat Pham <nphamcs@...il.com>, Johannes Weiner <hannes@...xchg.org>, Andrew Morton <akpm@...ux-foundation.org>,
 Yosry Ahmed <yosryahmed@...gle.com>
Cc: linux-kernel@...r.kernel.org, Yosry Ahmed <yosryahmed@...gle.com>, Chengming Zhou <zhouchengming@...edance.com>,
 Johannes Weiner <hannes@...xchg.org>, linux-mm@...ck.org
Subject: [PATCH 4/6] mm/zswap: remove duplicate_entry debug value

cat /sys/kernel/debug/zswap/duplicate_entry
2086447

When testing, the duplicate_entry value is very high, but no warning
message in the kernel log. From the comment of duplicate_entry
"Duplicate store was encountered (rare)", it seems something goes wrong.

Actually it's incremented in the beginning of zswap_store(), which found
its zswap entry has already on the tree. And this is a normal case,
since the folio could leave zswap entry on the tree after swapin,
later it's dirtied and swapout/zswap_store again, found its original
zswap entry. (Maybe we can reuse it instead of invalidating it?)

So duplicate_entry should be only incremented in the real bug case,
which already have "WARN_ON(1)", it looks redundant to count bug case,
so this patch just remove it.

Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
---
 mm/zswap.c | 9 +--------
 1 file changed, 1 insertion(+), 8 deletions(-)

diff --git a/mm/zswap.c b/mm/zswap.c
index 4381b7a2d4d6..3fbb7e2c8b8d 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -71,8 +71,6 @@ static u64 zswap_reject_compress_poor;
 static u64 zswap_reject_alloc_fail;
 /* Store failed because the entry metadata could not be allocated (rare) */
 static u64 zswap_reject_kmemcache_fail;
-/* Duplicate store was encountered (rare) */
-static u64 zswap_duplicate_entry;
 
 /* Shrinker work queue */
 static struct workqueue_struct *shrink_wq;
@@ -1571,10 +1569,8 @@ bool zswap_store(struct folio *folio)
 	 */
 	spin_lock(&tree->lock);
 	entry = zswap_rb_search(&tree->rbroot, offset);
-	if (entry) {
+	if (entry)
 		zswap_invalidate_entry(tree, entry);
-		zswap_duplicate_entry++;
-	}
 	spin_unlock(&tree->lock);
 	objcg = get_obj_cgroup_from_folio(folio);
 	if (objcg && !obj_cgroup_may_zswap(objcg)) {
@@ -1661,7 +1657,6 @@ bool zswap_store(struct folio *folio)
 	 */
 	while (zswap_rb_insert(&tree->rbroot, entry, &dupentry) == -EEXIST) {
 		WARN_ON(1);
-		zswap_duplicate_entry++;
 		zswap_invalidate_entry(tree, dupentry);
 	}
 	if (entry->length) {
@@ -1822,8 +1817,6 @@ static int zswap_debugfs_init(void)
 			   zswap_debugfs_root, &zswap_reject_compress_poor);
 	debugfs_create_u64("written_back_pages", 0444,
 			   zswap_debugfs_root, &zswap_written_back_pages);
-	debugfs_create_u64("duplicate_entry", 0444,
-			   zswap_debugfs_root, &zswap_duplicate_entry);
 	debugfs_create_u64("pool_total_size", 0444,
 			   zswap_debugfs_root, &zswap_pool_total_size);
 	debugfs_create_atomic_t("stored_pages", 0444,

-- 
b4 0.10.1