[PATCH] mm: add per-order mTHP swap-in fallback counters

[Wenchao Hao <haowenchao22@gmail.com>]

Now large folio swap-in is supported, but we do not have a method
to analyze the success ratio of large folio swap-ins. Similar to
anon_fault_fallback, we add a per-order mTHP swpin_fallback to help
calculate the success ratio. The new counter is located at:

/sys/kernel/mm/transparent_hugepage/hugepages-<size>/stats/swpin_fallback

Signed-off-by: Wenchao Hao <haowenchao22@gmail.com>
CC: Chuanhua Han <hanchuanhua@oppo.com>
---
 Documentation/admin-guide/mm/transhuge.rst | 5 +++++
 include/linux/huge_mm.h                    | 1 +
 mm/huge_memory.c                           | 3 +++
 mm/memory.c                                | 1 +
 4 files changed, 10 insertions(+)

diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst
index 5034915f4e8e..f5c775457913 100644
--- a/Documentation/admin-guide/mm/transhuge.rst
+++ b/Documentation/admin-guide/mm/transhuge.rst
@@ -561,6 +561,11 @@ swpin
 	is incremented every time a huge page is swapped in from a non-zswap
 	swap device in one piece.
 
+swpin_fallback
+	is incremented if a huge page swapin fails to allocate a huge page
+	and instead falls back to using huge pages with lower orders or
+	small pages.
+
 swpout
 	is incremented every time a huge page is swapped out to a non-zswap
 	swap device in one piece without splitting.
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index b94c2e8ee918..dcf08f8fdf52 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -121,6 +121,7 @@ enum mthp_stat_item {
 	MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE,
 	MTHP_STAT_ZSWPOUT,
 	MTHP_STAT_SWPIN,
+	MTHP_STAT_SWPIN_FALLBACK,
 	MTHP_STAT_SWPOUT,
 	MTHP_STAT_SWPOUT_FALLBACK,
 	MTHP_STAT_SHMEM_ALLOC,
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index ee335d96fc39..6b089a41acef 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -617,6 +617,7 @@ 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(swpin, MTHP_STAT_SWPIN);
+DEFINE_MTHP_STAT_ATTR(swpin_fallback, MTHP_STAT_SWPIN_FALLBACK);
 DEFINE_MTHP_STAT_ATTR(swpout, MTHP_STAT_SWPOUT);
 DEFINE_MTHP_STAT_ATTR(swpout_fallback, MTHP_STAT_SWPOUT_FALLBACK);
 #ifdef CONFIG_SHMEM
@@ -637,6 +638,7 @@ static struct attribute *anon_stats_attrs[] = {
 #ifndef CONFIG_SHMEM
 	&zswpout_attr.attr,
 	&swpin_attr.attr,
+	&swpin_fallback_attr.attr,
 	&swpout_attr.attr,
 	&swpout_fallback_attr.attr,
 #endif
@@ -669,6 +671,7 @@ static struct attribute *any_stats_attrs[] = {
 #ifdef CONFIG_SHMEM
 	&zswpout_attr.attr,
 	&swpin_attr.attr,
+	&swpin_fallback_attr.attr,
 	&swpout_attr.attr,
 	&swpout_fallback_attr.attr,
 #endif
diff --git a/mm/memory.c b/mm/memory.c
index 209885a4134f..7cda8b65e0c9 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4191,6 +4191,7 @@ static struct folio *alloc_swap_folio(struct vm_fault *vmf)
 				return folio;
 			folio_put(folio);
 		}
+		count_mthp_stat(order, MTHP_STAT_SWPIN_FALLBACK);
 		order = next_order(&orders, order);
 	}
 
-- 
2.45.0