[PATCH v3 4/4] mm: swap: Count successful mTHP ZSWAP stores in sysfs mTHP stats.

[Kanchana P Sridhar <kanchana.p.sridhar@intel.com>]

If zswap_store() successfully stores 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>
---
 mm/page_io.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/mm/page_io.c b/mm/page_io.c
index ff8c99ee3af7..debd04fbdfd0 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -172,6 +172,12 @@ int generic_swapfile_activate(struct swap_info_struct *sis,
 	goto out;
 }
 
+static inline void count_mthp_zswpout_vm_event(struct folio *folio)
+{
+	if (IS_ENABLED(CONFIG_THP_SWAP))
+		count_mthp_stat(folio_order(folio), MTHP_STAT_ZSWPOUT);
+}
+
 /*
  * We may have stale swap cache pages in memory: notice
  * them here and get rid of the unnecessary final write.
@@ -196,6 +202,7 @@ int swap_writepage(struct page *page, struct writeback_control *wbc)
 		return ret;
 	}
 	if (zswap_store(folio)) {
+		count_mthp_zswpout_vm_event(folio);
 		folio_unlock(folio);
 		return 0;
 	}
-- 
2.27.0