mm: zswap: add basic meminfo and vmstat coverage

Currently it requires poking at debugfs to figure out the size and
population of the zswap cache on a host.  There are no counters for reads
and writes against the cache.  As a result, it's difficult to understand
zswap behavior on production systems.

Print zswap memory consumption and how many pages are zswapped out in
/proc/meminfo.  Count zswapouts and zswapins in /proc/vmstat.

Link: https://lkml.kernel.org/r/20220510152847.230957-6-hannes@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Dan Streetman <ddstreet@ieee.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Roman Gushchin <guro@fb.com>
Cc: Seth Jennings <sjenning@redhat.com>
Cc: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

2 files changed, 10 insertions, 7 deletions

diff --git a/mm/vmstat.c b/mm/vmstat.c
index b94a2e4723ff..da525bfb6f4a 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1396,6 +1396,10 @@ const char * const vmstat_text[] = {
 #ifdef CONFIG_KSM
 	"cow_ksm",
 #endif
+#ifdef CONFIG_ZSWAP
+	"zswpin",
+	"zswpout",
+#endif
 #ifdef CONFIG_X86
 	"direct_map_level2_splits",
 	"direct_map_level3_splits",
diff --git a/mm/zswap.c b/mm/zswap.c
index 2c5db4cbedea..e3c16a70f533 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -42,9 +42,9 @@
 * statistics
 **********************************/
 /* Total bytes used by the compressed storage */
-static u64 zswap_pool_total_size;
+u64 zswap_pool_total_size;
 /* The number of compressed pages currently stored in zswap */
-static atomic_t zswap_stored_pages = ATOMIC_INIT(0);
+atomic_t zswap_stored_pages = ATOMIC_INIT(0);
 /* The number of same-value filled pages currently stored in zswap */
 static atomic_t zswap_same_filled_pages = ATOMIC_INIT(0);
 
@@ -1243,6 +1243,7 @@ insert_entry:
 	/* update stats */
 	atomic_inc(&zswap_stored_pages);
 	zswap_update_total_size();
+	count_vm_event(ZSWPOUT);
 
 	return 0;
 
@@ -1285,11 +1286,10 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
 		zswap_fill_page(dst, entry->value);
 		kunmap_atomic(dst);
 		ret = 0;
-		goto freeentry;
+		goto stats;
 	}
 
 	if (!zpool_can_sleep_mapped(entry->pool->zpool)) {
-
 		tmp = kmalloc(entry->length, GFP_ATOMIC);
 		if (!tmp) {
 			ret = -ENOMEM;
@@ -1304,10 +1304,8 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
 		src += sizeof(struct zswap_header);
 
 	if (!zpool_can_sleep_mapped(entry->pool->zpool)) {
-
 		memcpy(tmp, src, entry->length);
 		src = tmp;
-
 		zpool_unmap_handle(entry->pool->zpool, entry->handle);
 	}
 
@@ -1326,7 +1324,8 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
 		kfree(tmp);
 
 	BUG_ON(ret);
-
+stats:
+	count_vm_event(ZSWPIN);
 freeentry:
 	spin_lock(&tree->lock);
 	zswap_entry_put(tree, entry);