[PATCH 1/2] mm: add per-order mTHP split counters

[Lance Yang <ioworker0@gmail.com>]

At present, the split counters in THP statistics no longer include
PTE-mapped mTHP. Therefore, this commit introduces per-order mTHP split
counters to monitor the frequency of mTHP splits. This will assist
developers in better analyzing and optimizing system performance.

/sys/kernel/mm/transparent_hugepage/hugepages-<size>/stats
        split_page
        split_page_failed
        deferred_split_page

Signed-off-by: Lance Yang <ioworker0@gmail.com>
---
 include/linux/huge_mm.h |  3 +++
 mm/huge_memory.c        | 14 ++++++++++++--
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 56c7ea73090b..7b9c6590e1f7 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -272,6 +272,9 @@ enum mthp_stat_item {
 	MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE,
 	MTHP_STAT_ANON_SWPOUT,
 	MTHP_STAT_ANON_SWPOUT_FALLBACK,
+	MTHP_STAT_SPLIT_PAGE,
+	MTHP_STAT_SPLIT_PAGE_FAILED,
+	MTHP_STAT_DEFERRED_SPLIT_PAGE,
 	__MTHP_STAT_COUNT
 };
 
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 055df5aac7c3..52db888e47a6 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -557,6 +557,9 @@ 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(anon_swpout, MTHP_STAT_ANON_SWPOUT);
 DEFINE_MTHP_STAT_ATTR(anon_swpout_fallback, MTHP_STAT_ANON_SWPOUT_FALLBACK);
+DEFINE_MTHP_STAT_ATTR(split_page, MTHP_STAT_SPLIT_PAGE);
+DEFINE_MTHP_STAT_ATTR(split_page_failed, MTHP_STAT_SPLIT_PAGE_FAILED);
+DEFINE_MTHP_STAT_ATTR(deferred_split_page, MTHP_STAT_DEFERRED_SPLIT_PAGE);
 
 static struct attribute *stats_attrs[] = {
 	&anon_fault_alloc_attr.attr,
@@ -564,6 +567,9 @@ static struct attribute *stats_attrs[] = {
 	&anon_fault_fallback_charge_attr.attr,
 	&anon_swpout_attr.attr,
 	&anon_swpout_fallback_attr.attr,
+	&split_page_attr.attr,
+	&split_page_failed_attr.attr,
+	&deferred_split_page_attr.attr,
 	NULL,
 };
 
@@ -3083,7 +3089,7 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
 	XA_STATE_ORDER(xas, &folio->mapping->i_pages, folio->index, new_order);
 	struct anon_vma *anon_vma = NULL;
 	struct address_space *mapping = NULL;
-	bool is_thp = folio_test_pmd_mappable(folio);
+	int order = folio_order(folio);
 	int extra_pins, ret;
 	pgoff_t end;
 	bool is_hzp;
@@ -3262,8 +3268,10 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
 		i_mmap_unlock_read(mapping);
 out:
 	xas_destroy(&xas);
-	if (is_thp)
+	if (order >= HPAGE_PMD_ORDER)
 		count_vm_event(!ret ? THP_SPLIT_PAGE : THP_SPLIT_PAGE_FAILED);
+	count_mthp_stat(order, !ret ? MTHP_STAT_SPLIT_PAGE :
+				      MTHP_STAT_SPLIT_PAGE_FAILED);
 	return ret;
 }
 
@@ -3327,6 +3335,8 @@ void deferred_split_folio(struct folio *folio)
 	if (list_empty(&folio->_deferred_list)) {
 		if (folio_test_pmd_mappable(folio))
 			count_vm_event(THP_DEFERRED_SPLIT_PAGE);
+		count_mthp_stat(folio_order(folio),
+				MTHP_STAT_DEFERRED_SPLIT_PAGE);
 		list_add_tail(&folio->_deferred_list, &ds_queue->split_queue);
 		ds_queue->split_queue_len++;
 #ifdef CONFIG_MEMCG
-- 
2.33.1