linux-kernel - [PATCH 4/4] mm: zswap: add basic meminfo and vmstat coverage

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Date:   Thu, 19 Aug 2021 15:55:33 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kernel-team@...com
Subject: [PATCH 4/4] mm: zswap: add basic meminfo and vmstat coverage

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

Print zswap memory consumption in /proc/meminfo, count zswapouts and
zswapins in /proc/vmstat.

Signed-off-by: Johannes Weiner <hannes@...xchg.org>
---
 fs/proc/meminfo.c             |  4 ++++
 include/linux/swap.h          |  4 ++++
 include/linux/vm_event_item.h |  4 ++++
 mm/vmstat.c                   |  4 ++++
 mm/zswap.c                    | 11 +++++------
 5 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/fs/proc/meminfo.c b/fs/proc/meminfo.c
index 6fa761c9cc78..2dc474940691 100644
--- a/fs/proc/meminfo.c
+++ b/fs/proc/meminfo.c
@@ -86,6 +86,10 @@ static int meminfo_proc_show(struct seq_file *m, void *v)
 
 	show_val_kb(m, "SwapTotal:      ", i.totalswap);
 	show_val_kb(m, "SwapFree:       ", i.freeswap);
+#ifdef CONFIG_ZSWAP
+	seq_printf(m,  "Zswap:          %8lu kB\n",
+		   (unsigned long)(zswap_pool_total_size >> 10));
+#endif
 	show_val_kb(m, "Dirty:          ",
 		    global_node_page_state(NR_FILE_DIRTY));
 	show_val_kb(m, "Writeback:      ",
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 144727041e78..3b23c88b6a8d 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -696,6 +696,10 @@ static inline int mem_cgroup_swappiness(struct mem_cgroup *mem)
 }
 #endif
 
+#ifdef CONFIG_ZSWAP
+extern u64 zswap_pool_total_size;
+#endif
+
 #if defined(CONFIG_SWAP) && defined(CONFIG_MEMCG) && defined(CONFIG_BLK_CGROUP)
 extern void cgroup_throttle_swaprate(struct page *page, gfp_t gfp_mask);
 #else
diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
index ae0dd1948c2b..9dbebea09c69 100644
--- a/include/linux/vm_event_item.h
+++ b/include/linux/vm_event_item.h
@@ -125,6 +125,10 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
 		SWAP_RA,
 		SWAP_RA_HIT,
 #endif
+#ifdef CONFIG_ZSWAP
+		ZSWPIN,
+		ZSWPOUT,
+#endif
 #ifdef CONFIG_X86
 		DIRECT_MAP_LEVEL2_SPLIT,
 		DIRECT_MAP_LEVEL3_SPLIT,
diff --git a/mm/vmstat.c b/mm/vmstat.c
index cccee36b289c..31aada15c571 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1369,6 +1369,10 @@ const char * const vmstat_text[] = {
 	"swap_ra",
 	"swap_ra_hit",
 #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 20763267a219..f93a7c715f76 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -40,7 +40,7 @@
 * 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);
 /* The number of same-value filled pages currently stored in zswap */
@@ -1231,6 +1231,7 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
 	/* update stats */
 	atomic_inc(&zswap_stored_pages);
 	zswap_update_total_size();
+	count_vm_event(ZSWAPOUT);
 
 	return 0;
 
@@ -1273,11 +1274,10 @@ 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;
@@ -1292,10 +1292,8 @@ 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);
 	}
 
@@ -1314,7 +1312,8 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset,
 		kfree(tmp);
 
 	BUG_ON(ret);
-
+stats:
+	count_vm_event(ZSWAPIN);
 freeentry:
 	spin_lock(&tree->lock);
 	zswap_entry_put(tree, entry);
-- 
2.32.0