[PATCH v2 1/2] mm: add per-order mTHP split counters

[Lance Yang <ioworker0@gmail.com>]

Currently, the split counters in THP statistics no longer include
PTE-mapped mTHP. Therefore, we propose introducing per-order mTHP split
counters to monitor the frequency of mTHP splits. This will help developers
better analyze and optimize system performance.

/sys/kernel/mm/transparent_hugepage/hugepages-<size>/stats
        split
        split_failed
        split_deferred

Signed-off-by: Mingzhe Yang <mingzhe.yang@ly.com>
Signed-off-by: Lance Yang <ioworker0@gmail.com>
---
 include/linux/huge_mm.h |  3 +++
 mm/huge_memory.c        | 19 ++++++++++++++-----
 2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 212cca384d7e..cee3c5da8f0e 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -284,6 +284,9 @@ enum mthp_stat_item {
 	MTHP_STAT_FILE_ALLOC,
 	MTHP_STAT_FILE_FALLBACK,
 	MTHP_STAT_FILE_FALLBACK_CHARGE,
+	MTHP_STAT_SPLIT,
+	MTHP_STAT_SPLIT_FAILED,
+	MTHP_STAT_SPLIT_DEFERRED,
 	__MTHP_STAT_COUNT
 };
 
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index c7ce28f6b7f3..a633206375af 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -559,6 +559,9 @@ DEFINE_MTHP_STAT_ATTR(swpout_fallback, MTHP_STAT_SWPOUT_FALLBACK);
 DEFINE_MTHP_STAT_ATTR(file_alloc, MTHP_STAT_FILE_ALLOC);
 DEFINE_MTHP_STAT_ATTR(file_fallback, MTHP_STAT_FILE_FALLBACK);
 DEFINE_MTHP_STAT_ATTR(file_fallback_charge, MTHP_STAT_FILE_FALLBACK_CHARGE);
+DEFINE_MTHP_STAT_ATTR(split, MTHP_STAT_SPLIT);
+DEFINE_MTHP_STAT_ATTR(split_failed, MTHP_STAT_SPLIT_FAILED);
+DEFINE_MTHP_STAT_ATTR(split_deferred, MTHP_STAT_SPLIT_DEFERRED);
 
 static struct attribute *stats_attrs[] = {
 	&anon_fault_alloc_attr.attr,
@@ -569,6 +572,9 @@ static struct attribute *stats_attrs[] = {
 	&file_alloc_attr.attr,
 	&file_fallback_attr.attr,
 	&file_fallback_charge_attr.attr,
+	&split_attr.attr,
+	&split_failed_attr.attr,
+	&split_deferred_attr.attr,
 	NULL,
 };
 
@@ -3068,7 +3074,7 @@ 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;
@@ -3076,7 +3082,7 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
 	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
 	VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
 
-	if (new_order >= folio_order(folio))
+	if (new_order >= order)
 		return -EINVAL;
 
 	if (folio_test_anon(folio)) {
@@ -3253,8 +3259,9 @@ 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 : MTHP_STAT_SPLIT_FAILED);
 	return ret;
 }
 
@@ -3278,13 +3285,14 @@ void deferred_split_folio(struct folio *folio)
 #ifdef CONFIG_MEMCG
 	struct mem_cgroup *memcg = folio_memcg(folio);
 #endif
+	int order = folio_order(folio);
 	unsigned long flags;
 
 	/*
 	 * Order 1 folios have no space for a deferred list, but we also
 	 * won't waste much memory by not adding them to the deferred list.
 	 */
-	if (folio_order(folio) <= 1)
+	if (order <= 1)
 		return;
 
 	/*
@@ -3305,8 +3313,9 @@ void deferred_split_folio(struct folio *folio)
 
 	spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
 	if (list_empty(&folio->_deferred_list)) {
-		if (folio_test_pmd_mappable(folio))
+		if (order >= HPAGE_PMD_ORDER)
 			count_vm_event(THP_DEFERRED_SPLIT_PAGE);
+		count_mthp_stat(order, MTHP_STAT_SPLIT_DEFERRED);
 		list_add_tail(&folio->_deferred_list, &ds_queue->split_queue);
 		ds_queue->split_queue_len++;
 #ifdef CONFIG_MEMCG
-- 
2.45.2