Add a new MTHP_STAT_ZSWPOUT entry to the sysfs mTHP stats so that
per-order mTHP folio ZSWAP stores can be accounted.

If zswap_store() successfully swaps out an mTHP, it will be counted under
the per-order sysfs "zswpout" stats:

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

Other block dev/fs mTHP swap-out events will be counted under
the existing sysfs "swpout" stats:

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

Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@intel.com>
---
 include/linux/huge_mm.h | 1 +
 mm/huge_memory.c        | 3 +++
 mm/page_io.c            | 1 +
 3 files changed, 5 insertions(+)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 0b0539f4ee1a..ab95b94e9627 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -118,6 +118,7 @@ enum mthp_stat_item {
 	MTHP_STAT_ANON_FAULT_ALLOC,
 	MTHP_STAT_ANON_FAULT_FALLBACK,
 	MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE,
+	MTHP_STAT_ZSWPOUT,
 	MTHP_STAT_SWPOUT,
 	MTHP_STAT_SWPOUT_FALLBACK,
 	MTHP_STAT_SHMEM_ALLOC,
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 4e34b7f89daf..7d8ce7891ba8 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -612,6 +612,7 @@ static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
 DEFINE_MTHP_STAT_ATTR(anon_fault_alloc, MTHP_STAT_ANON_FAULT_ALLOC);
 DEFINE_MTHP_STAT_ATTR(anon_fault_fallback, MTHP_STAT_ANON_FAULT_FALLBACK);
 DEFINE_MTHP_STAT_ATTR(anon_fault_fallback_charge, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE);
+DEFINE_MTHP_STAT_ATTR(zswpout, MTHP_STAT_ZSWPOUT);
 DEFINE_MTHP_STAT_ATTR(swpout, MTHP_STAT_SWPOUT);
 DEFINE_MTHP_STAT_ATTR(swpout_fallback, MTHP_STAT_SWPOUT_FALLBACK);
 #ifdef CONFIG_SHMEM
@@ -630,6 +631,7 @@ static struct attribute *anon_stats_attrs[] = {
 	&anon_fault_fallback_attr.attr,
 	&anon_fault_fallback_charge_attr.attr,
 #ifndef CONFIG_SHMEM
+	&zswpout_attr.attr,
 	&swpout_attr.attr,
 	&swpout_fallback_attr.attr,
 #endif
@@ -660,6 +662,7 @@ static struct attribute_group file_stats_attr_grp = {
 
 static struct attribute *any_stats_attrs[] = {
 #ifdef CONFIG_SHMEM
+	&zswpout_attr.attr,
 	&swpout_attr.attr,
 	&swpout_fallback_attr.attr,
 #endif
diff --git a/mm/page_io.c b/mm/page_io.c
index bc1183299a7d..4aa34862676f 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -269,6 +269,7 @@ int swap_writepage(struct page *page, struct writeback_control *wbc)
 		swap_zeromap_folio_clear(folio);
 	}
 	if (zswap_store(folio)) {
+		count_mthp_stat(folio_order(folio), MTHP_STAT_ZSWPOUT);
 		folio_unlock(folio);
 		return 0;
 	}
-- 
2.27.0