[PATCH v6 1/4] mm: add per-order mTHP anon_fault_alloc and anon_fault_fallback counters

[Barry Song]

From: Barry Song <v-songbaohua@xxxxxxxx>

Profiling a system blindly with mTHP has become challenging due to the
lack of visibility into its operations.  Presenting the success rate of
mTHP allocations appears to be pressing need.

Recently, I've been experiencing significant difficulty debugging
performance improvements and regressions without these figures.  It's
crucial for us to understand the true effectiveness of mTHP in real-world
scenarios, especially in systems with fragmented memory.

This patch establishes the framework for per-order mTHP
counters. It begins by introducing the anon_fault_alloc and
anon_fault_fallback counters. Additionally, to maintain consistency
with thp_fault_fallback_charge in /proc/vmstat, this patch also tracks
anon_fault_fallback_charge when mem_cgroup_charge fails for mTHP.
Incorporating additional counters should now be straightforward as well.

Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>
Cc: Chris Li <chrisl@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Domenico Cerasuolo <cerasuolodomenico@xxxxxxxxx>
Cc: Kairui Song <kasong@xxxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Cc: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
---
 include/linux/huge_mm.h | 21 +++++++++++++++++
 mm/huge_memory.c        | 52 +++++++++++++++++++++++++++++++++++++++++
 mm/memory.c             |  5 ++++
 3 files changed, 78 insertions(+)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index e896ca4760f6..d4fdb2641070 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -264,6 +264,27 @@ unsigned long thp_vma_allowable_orders(struct vm_area_struct *vma,
 					  enforce_sysfs, orders);
 }
 
+enum mthp_stat_item {
+	MTHP_STAT_ANON_FAULT_ALLOC,
+	MTHP_STAT_ANON_FAULT_FALLBACK,
+	MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE,
+	__MTHP_STAT_COUNT
+};
+
+struct mthp_stat {
+	unsigned long stats[ilog2(MAX_PTRS_PER_PTE) + 1][__MTHP_STAT_COUNT];
+};
+
+DECLARE_PER_CPU(struct mthp_stat, mthp_stats);
+
+static inline void count_mthp_stat(int order, enum mthp_stat_item item)
+{
+	if (order <= 0 || order > PMD_ORDER)
+		return;
+
+	this_cpu_inc(mthp_stats.stats[order][item]);
+}
+
 #define transparent_hugepage_use_zero_page()				\
 	(transparent_hugepage_flags &					\
 	 (1<<TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG))
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index dc30139590e6..dfc38cc83a04 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -526,6 +526,48 @@ static const struct kobj_type thpsize_ktype = {
 	.sysfs_ops = &kobj_sysfs_ops,
 };
 
+DEFINE_PER_CPU(struct mthp_stat, mthp_stats) = {{{0}}};
+
+static unsigned long sum_mthp_stat(int order, enum mthp_stat_item item)
+{
+	unsigned long sum = 0;
+	int cpu;
+
+	for_each_possible_cpu(cpu) {
+		struct mthp_stat *this = &per_cpu(mthp_stats, cpu);
+
+		sum += this->stats[order][item];
+	}
+
+	return sum;
+}
+
+#define DEFINE_MTHP_STAT_ATTR(_name, _index)				\
+static ssize_t _name##_show(struct kobject *kobj,			\
+			struct kobj_attribute *attr, char *buf)		\
+{									\
+	int order = to_thpsize(kobj)->order;				\
+									\
+	return sysfs_emit(buf, "%lu\n", sum_mthp_stat(order, _index));	\
+}									\
+static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
+
+DEFINE_MTHP_STAT_ATTR(anon_fault_alloc, MTHP_STAT_ANON_FAULT_ALLOC);
+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);
+
+static struct attribute *stats_attrs[] = {
+	&anon_fault_alloc_attr.attr,
+	&anon_fault_fallback_attr.attr,
+	&anon_fault_fallback_charge_attr.attr,
+	NULL,
+};
+
+static struct attribute_group stats_attr_group = {
+	.name = "stats",
+	.attrs = stats_attrs,
+};
+
 static struct thpsize *thpsize_create(int order, struct kobject *parent)
 {
 	unsigned long size = (PAGE_SIZE << order) / SZ_1K;
@@ -549,6 +591,12 @@ static struct thpsize *thpsize_create(int order, struct kobject *parent)
 		return ERR_PTR(ret);
 	}
 
+	ret = sysfs_create_group(&thpsize->kobj, &stats_attr_group);
+	if (ret) {
+		kobject_put(&thpsize->kobj);
+		return ERR_PTR(ret);
+	}
+
 	thpsize->order = order;
 	return thpsize;
 }
@@ -880,6 +928,8 @@ static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf,
 		folio_put(folio);
 		count_vm_event(THP_FAULT_FALLBACK);
 		count_vm_event(THP_FAULT_FALLBACK_CHARGE);
+		count_mthp_stat(HPAGE_PMD_ORDER, MTHP_STAT_ANON_FAULT_FALLBACK);
+		count_mthp_stat(HPAGE_PMD_ORDER, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE);
 		return VM_FAULT_FALLBACK;
 	}
 	folio_throttle_swaprate(folio, gfp);
@@ -929,6 +979,7 @@ static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf,
 		mm_inc_nr_ptes(vma->vm_mm);
 		spin_unlock(vmf->ptl);
 		count_vm_event(THP_FAULT_ALLOC);
+		count_mthp_stat(HPAGE_PMD_ORDER, MTHP_STAT_ANON_FAULT_ALLOC);
 		count_memcg_event_mm(vma->vm_mm, THP_FAULT_ALLOC);
 	}
 
@@ -1050,6 +1101,7 @@ vm_fault_t do_huge_pmd_anonymous_page(struct vm_fault *vmf)
 	folio = vma_alloc_folio(gfp, HPAGE_PMD_ORDER, vma, haddr, true);
 	if (unlikely(!folio)) {
 		count_vm_event(THP_FAULT_FALLBACK);
+		count_mthp_stat(HPAGE_PMD_ORDER, MTHP_STAT_ANON_FAULT_FALLBACK);
 		return VM_FAULT_FALLBACK;
 	}
 	return __do_huge_pmd_anonymous_page(vmf, &folio->page, gfp);
diff --git a/mm/memory.c b/mm/memory.c
index 649a547fe8e3..f31da2de19c6 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4368,6 +4368,7 @@ static struct folio *alloc_anon_folio(struct vm_fault *vmf)
 		folio = vma_alloc_folio(gfp, order, vma, addr, true);
 		if (folio) {
 			if (mem_cgroup_charge(folio, vma->vm_mm, gfp)) {
+				count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE);
 				folio_put(folio);
 				goto next;
 			}
@@ -4376,6 +4377,7 @@ static struct folio *alloc_anon_folio(struct vm_fault *vmf)
 			return folio;
 		}
 next:
+		count_mthp_stat(order, MTHP_STAT_ANON_FAULT_FALLBACK);
 		order = next_order(&orders, order);
 	}
 
@@ -4485,6 +4487,9 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
 
 	folio_ref_add(folio, nr_pages - 1);
 	add_mm_counter(vma->vm_mm, MM_ANONPAGES, nr_pages);
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+	count_mthp_stat(folio_order(folio), MTHP_STAT_ANON_FAULT_ALLOC);
+#endif
 	folio_add_new_anon_rmap(folio, vma, addr);
 	folio_add_lru_vma(folio, vma);
 setpte:
-- 
2.34.1