[PATCH 4/5] mm: zswap: add basic meminfo and vmstat coverage

Johannes Weiner
2022-04-27T16:00:15Z

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.

Signed-off-by: Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>
---
fs/proc/meminfo.c | 7 +++++++
include/linux/swap.h | 5 +++++
include/linux/vm_event_item.h | 4 ++++
mm/vmstat.c | 4 ++++
mm/zswap.c | 13 ++++++-------
5 files changed, 26 insertions(+), 7 deletions(-)

diff --git a/fs/proc/meminfo.c b/fs/proc/meminfo.c
index 6fa761c9cc78..6e89f0e2fd20 100644
--- a/fs/proc/meminfo.c
+++ b/fs/proc/meminfo.c
@@ -86,6 +86,13 @@ 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));
+ seq_printf(m, "Zswapped: %8lu kB\n",
+ (unsigned long)atomic_read(&zswap_stored_pages) <<
+ (PAGE_SHIFT - 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 b82c196d8867..07074afa79a7 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -632,6 +632,11 @@ static inline int mem_cgroup_swappiness(struct mem_cgroup *mem)
}
#endif

+#ifdef CONFIG_ZSWAP
+extern u64 zswap_pool_total_size;
+extern atomic_t zswap_stored_pages;
+#endif
+
#if defined(CONFIG_SWAP) && defined(CONFIG_MEMCG) && defined(CONFIG_BLK_CGROUP)
extern void __cgroup_throttle_swaprate(struct page *page, gfp_t gfp_mask);
static inline void cgroup_throttle_swaprate(struct page *page, gfp_t gfp_mask)
diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
index 5e80138ce624..1ce8fadb2b1c 100644
--- a/include/linux/vm_event_item.h
+++ b/include/linux/vm_event_item.h
@@ -132,6 +132,10 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
#ifdef CONFIG_KSM
COW_KSM,
#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 4a2aa2fa88db..da7e389cf33c 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1392,6 +1392,10 @@ 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 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
/* 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);
--
2.35.3