[RFC PATCH v1 4/4] mm: page_io: Count successful mTHP zswap stores in vmstat.

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

Added count_zswap_thp_swpout_vm_event() that will increment the
appropriate mTHP/PMD vmstat event counters if zswap_store succeeds for
a large folio:

zswap_store mTHP order [0, HPAGE_PMD_ORDER-1] will increment these
vmstat event counters:

  ZSWPOUT_4KB_FOLIO
  mTHP_ZSWPOUT_8kB
  mTHP_ZSWPOUT_16kB
  mTHP_ZSWPOUT_32kB
  mTHP_ZSWPOUT_64kB
  mTHP_ZSWPOUT_128kB
  mTHP_ZSWPOUT_256kB
  mTHP_ZSWPOUT_512kB
  mTHP_ZSWPOUT_1024kB

zswap_store of a PMD-size THP, i.e., mTHP order HPAGE_PMD_ORDER, will
increment both these vmstat event counters:

  ZSWPOUT_PMD_THP_FOLIO
  mTHP_ZSWPOUT_2048kB

Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@xxxxxxxxx>
---
 mm/page_io.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/mm/page_io.c b/mm/page_io.c
index 0a150c240bf4..ab54d2060cc4 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -172,6 +172,49 @@ int generic_swapfile_activate(struct swap_info_struct *sis,
 	goto out;
 }
 
+/*
+ * Count vmstats for ZSWAP store of large folios (mTHP and PMD-size THP).
+ */
+static inline void count_zswap_thp_swpout_vm_event(struct folio *folio)
+{
+	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && folio_test_pmd_mappable(folio)) {
+		count_vm_event(ZSWPOUT_PMD_THP_FOLIO);
+		count_vm_event(mTHP_ZSWPOUT_2048kB);
+	} else if (folio_order(folio) == 0) {
+		count_vm_event(ZSWPOUT_4KB_FOLIO);
+	} else if (IS_ENABLED(CONFIG_THP_SWAP)) {
+		switch (folio_order(folio)) {
+		case 1:
+			count_vm_event(mTHP_ZSWPOUT_8kB);
+			break;
+		case 2:
+			count_vm_event(mTHP_ZSWPOUT_16kB);
+			break;
+		case 3:
+			count_vm_event(mTHP_ZSWPOUT_32kB);
+			break;
+		case 4:
+			count_vm_event(mTHP_ZSWPOUT_64kB);
+			break;
+		case 5:
+			count_vm_event(mTHP_ZSWPOUT_128kB);
+			break;
+		case 6:
+			count_vm_event(mTHP_ZSWPOUT_256kB);
+			break;
+		case 7:
+			count_vm_event(mTHP_ZSWPOUT_512kB);
+			break;
+		case 8:
+			count_vm_event(mTHP_ZSWPOUT_1024kB);
+			break;
+		case 9:
+			count_vm_event(mTHP_ZSWPOUT_2048kB);
+			break;
+		}
+	}
+}
+
 /*
  * We may have stale swap cache pages in memory: notice
  * them here and get rid of the unnecessary final write.
@@ -196,6 +239,7 @@ int swap_writepage(struct page *page, struct writeback_control *wbc)
 		return ret;
 	}
 	if (zswap_store(folio)) {
+		count_zswap_thp_swpout_vm_event(folio);
 		folio_start_writeback(folio);
 		folio_unlock(folio);
 		folio_end_writeback(folio);
-- 
2.27.0