[PATCH 4/6] mm/zswap: remove duplicate_entry debug value

Chengming Zhou
2024-02-01T15:50:33Z

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@bytedance.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