[RFC PATCH v1 2/4] mm: vmstat: Per mTHP-size zswap_store vmstat event counters.

[Kanchana P Sridhar]

Added vmstat event counters per mTHP-size that can be used to account
for folios of different sizes being successfully stored in ZSWAP.

For this RFC, it is not clear if these zswpout counters should instead
be added as part of the existing mTHP stats in
/sys/kernel/mm/transparent_hugepage/hugepages-*kB/stats.

The following is also a viable option, should it make better sense,
for instance, as:

/sys/kernel/mm/transparent_hugepage/hugepages-*kB/stats/zswpout.

If so, we would be able to distinguish between mTHP zswap and
non-zswap swapouts through:

/sys/kernel/mm/transparent_hugepage/hugepages-*kB/stats/zswpout

and

/sys/kernel/mm/transparent_hugepage/hugepages-*kB/stats/swpout

respectively.

Comments would be appreciated as to which approach is preferable.

Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@xxxxxxxxx>
---
 include/linux/vm_event_item.h | 15 +++++++++++++++
 mm/vmstat.c                   | 15 +++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
index 747943bc8cc2..2451bcfcf05c 100644
--- a/include/linux/vm_event_item.h
+++ b/include/linux/vm_event_item.h
@@ -114,6 +114,9 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
 		THP_ZERO_PAGE_ALLOC,
 		THP_ZERO_PAGE_ALLOC_FAILED,
 		THP_SWPOUT,
+#ifdef CONFIG_ZSWAP
+		ZSWPOUT_PMD_THP_FOLIO,
+#endif
 		THP_SWPOUT_FALLBACK,
 #endif
 #ifdef CONFIG_MEMORY_BALLOON
@@ -143,6 +146,18 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
 		ZSWPIN,
 		ZSWPOUT,
 		ZSWPWB,
+		ZSWPOUT_4KB_FOLIO,
+#ifdef CONFIG_THP_SWAP
+		mTHP_ZSWPOUT_8kB,
+		mTHP_ZSWPOUT_16kB,
+		mTHP_ZSWPOUT_32kB,
+		mTHP_ZSWPOUT_64kB,
+		mTHP_ZSWPOUT_128kB,
+		mTHP_ZSWPOUT_256kB,
+		mTHP_ZSWPOUT_512kB,
+		mTHP_ZSWPOUT_1024kB,
+		mTHP_ZSWPOUT_2048kB,
+#endif
 #endif
 #ifdef CONFIG_X86
 		DIRECT_MAP_LEVEL2_SPLIT,
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 8507c497218b..0e66c8b0c486 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1375,6 +1375,9 @@ const char * const vmstat_text[] = {
 	"thp_zero_page_alloc",
 	"thp_zero_page_alloc_failed",
 	"thp_swpout",
+#ifdef CONFIG_ZSWAP
+	"zswpout_pmd_thp_folio",
+#endif
 	"thp_swpout_fallback",
 #endif
 #ifdef CONFIG_MEMORY_BALLOON
@@ -1405,6 +1408,18 @@ const char * const vmstat_text[] = {
 	"zswpin",
 	"zswpout",
 	"zswpwb",
+	"zswpout_4kb_folio",
+#ifdef CONFIG_THP_SWAP
+	"mthp_zswpout_8kb",
+	"mthp_zswpout_16kb",
+	"mthp_zswpout_32kb",
+	"mthp_zswpout_64kb",
+	"mthp_zswpout_128kb",
+	"mthp_zswpout_256kb",
+	"mthp_zswpout_512kb",
+	"mthp_zswpout_1024kb",
+	"mthp_zswpout_2048kb",
+#endif
 #endif
 #ifdef CONFIG_X86
 	"direct_map_level2_splits",
-- 
2.27.0