[PATCH] zswap: export more zswap store failure stats

[Nhat Pham <nphamcs@gmail.com>]

Since:

"42c06a0e8ebe mm: kill frontswap"

we no longer have a counter to tracks the number of zswap store
failures. This makes it hard to investigate and monitor for zswap
issues.

This patch adds a global and a per-cgroup zswap store failure counter,
as well as a dedicated debugfs counter for compression algorithm failure
(which can happen for e.g when random data are passed to zswap).

Signed-off-by: Nhat Pham <nphamcs@gmail.com>
---
 include/linux/vm_event_item.h |  1 +
 mm/memcontrol.c               |  1 +
 mm/vmstat.c                   |  1 +
 mm/zswap.c                    | 18 ++++++++++++++----
 4 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
index 8abfa1240040..7b2b117b193d 100644
--- a/include/linux/vm_event_item.h
+++ b/include/linux/vm_event_item.h
@@ -145,6 +145,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
 #ifdef CONFIG_ZSWAP
 		ZSWPIN,
 		ZSWPOUT,
+		ZSWPOUT_FAIL,
 #endif
 #ifdef CONFIG_X86
 		DIRECT_MAP_LEVEL2_SPLIT,
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 61c0c46c2d62..0e247e72a379 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -593,6 +593,7 @@ static const unsigned int memcg_vm_event_stat[] = {
 #if defined(CONFIG_MEMCG_KMEM) && defined(CONFIG_ZSWAP)
 	ZSWPIN,
 	ZSWPOUT,
+	ZSWPOUT_FAIL,
 #endif
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 	THP_FAULT_ALLOC,
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 359460deb377..85cc79449355 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1401,6 +1401,7 @@ const char * const vmstat_text[] = {
 #ifdef CONFIG_ZSWAP
 	"zswpin",
 	"zswpout",
+	"zswpout_fail",
 #endif
 #ifdef CONFIG_X86
 	"direct_map_level2_splits",
diff --git a/mm/zswap.c b/mm/zswap.c
index 37d2b1cb2ecb..38e6620f8b58 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -61,6 +61,8 @@ static u64 zswap_pool_limit_hit;
 static u64 zswap_written_back_pages;
 /* Store failed due to a reclaim failure after pool limit was reached */
 static u64 zswap_reject_reclaim_fail;
+/* Store failed due to compression algorithm failure */
+static u64 zswap_reject_compress_fail;
 /* Compressed page was too big for the allocator to (optimally) store */
 static u64 zswap_reject_compress_poor;
 /* Store failed because underlying allocator could not get memory */
@@ -1213,10 +1215,10 @@ bool zswap_store(struct folio *folio)
 
 	/* Large folios aren't supported */
 	if (folio_test_large(folio))
-		return false;
+		goto out_reject;
 
 	if (!zswap_enabled || !tree)
-		return false;
+		goto out_reject;
 
 	/*
 	 * If this is a duplicate, it must be removed before attempting to store
@@ -1309,8 +1311,10 @@ bool zswap_store(struct folio *folio)
 	ret = crypto_wait_req(crypto_acomp_compress(acomp_ctx->req), &acomp_ctx->wait);
 	dlen = acomp_ctx->req->dlen;
 
-	if (ret)
+	if (ret) {
+		zswap_reject_compress_fail++;
 		goto put_dstmem;
+	}
 
 	/* store */
 	zpool = zswap_find_zpool(entry);
@@ -1377,8 +1381,12 @@ bool zswap_store(struct folio *folio)
 freepage:
 	zswap_entry_cache_free(entry);
 reject:
-	if (objcg)
+	if (objcg) {
+		count_objcg_event(objcg, ZSWPOUT_FAIL);
 		obj_cgroup_put(objcg);
+	}
+out_reject:
+	count_vm_event(ZSWPOUT_FAIL);
 	return false;
 
 shrink:
@@ -1550,6 +1558,8 @@ static int zswap_debugfs_init(void)
 			   zswap_debugfs_root, &zswap_reject_alloc_fail);
 	debugfs_create_u64("reject_kmemcache_fail", 0444,
 			   zswap_debugfs_root, &zswap_reject_kmemcache_fail);
+	debugfs_create_u64("reject_compress_fail", 0444,
+			   zswap_debugfs_root, &zswap_reject_compress_fail);
 	debugfs_create_u64("reject_compress_poor", 0444,
 			   zswap_debugfs_root, &zswap_reject_compress_poor);
 	debugfs_create_u64("written_back_pages", 0444,
-- 
2.34.1