[RFC PATCH 3/4] mcpage: add vmstat counters for mcpages

[Yin Fengwei <fengwei.yin@xxxxxxxxx>]

MCPAGE_ANON_FAULT_ALLOC: how many times mcpage is used for anonymous
mapping.

MCPAGE_ANON_FAULT_FALLBACK: how many times fallback to normal page
for anonymous mapping.

MCPAGE_ANON_FAULT_CHARGE_FAILED: how many times fallback because of
memcg charge failure.

MCPAGE_ANON_FAULT_PAGE_TABLE_POPULATED: how many times fallback
because page table already populated.

MCPAGE_ANON_FAULT_INSTABLE_ADDRESS_SPACE: how many times fallback
because of unstable address space.

Signed-off-by: Yin Fengwei <fengwei.yin@xxxxxxxxx>
---
 include/linux/vm_event_item.h | 10 ++++++++++
 mm/mcpage_memory.c            |  6 ++++++
 mm/memory.c                   |  1 +
 mm/vmstat.c                   |  7 +++++++
 4 files changed, 24 insertions(+)

diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
index 7f5d1caf5890..9c36bfc4c904 100644
--- a/include/linux/vm_event_item.h
+++ b/include/linux/vm_event_item.h
@@ -119,6 +119,13 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
 		THP_SWPOUT,
 		THP_SWPOUT_FALLBACK,
 #endif
+#ifdef CONFIG_MCPAGE
+		MCPAGE_ANON_FAULT_ALLOC,
+		MCPAGE_ANON_FAULT_FALLBACK,
+		MCPAGE_ANON_FAULT_CHARGE_FAILED,
+		MCPAGE_ANON_FAULT_PAGE_TABLE_POPULATED,
+		MCPAGE_ANON_FAULT_INSTABLE_ADDRESS_SPACE,
+#endif
 #ifdef CONFIG_MEMORY_BALLOON
 		BALLOON_INFLATE,
 		BALLOON_DEFLATE,
@@ -159,5 +166,8 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
 #define THP_FILE_FALLBACK_CHARGE ({ BUILD_BUG(); 0; })
 #define THP_FILE_MAPPED ({ BUILD_BUG(); 0; })
 #endif
+#ifndef CONFIG_MCPAGE
+#define MCPAGE_ANON_FAULT_FALLBACK ({ BUILD_BUG(); 0; })
+#endif
 
 #endif		/* VM_EVENT_ITEM_H_INCLUDED */
diff --git a/mm/mcpage_memory.c b/mm/mcpage_memory.c
index ea4be2e25bce..e208cf818ebf 100644
--- a/mm/mcpage_memory.c
+++ b/mm/mcpage_memory.c
@@ -55,6 +55,7 @@ static vm_fault_t do_anonymous_mcpage(struct vm_fault *vmf,
 
 	if (mem_cgroup_charge(page_folio(page), vma->vm_mm, GFP_KERNEL)) {
 		ret = VM_FAULT_OOM;
+		count_vm_event(MCPAGE_ANON_FAULT_CHARGE_FAILED);
 		goto oom;
 	}
 
@@ -71,12 +72,14 @@ static vm_fault_t do_anonymous_mcpage(struct vm_fault *vmf,
 	if (!pte_none(*vmf->pte)) {
 		ret = VM_FAULT_FALLBACK;
 		update_mmu_cache(vma, addr, vmf->pte);
+		count_vm_event(MCPAGE_ANON_FAULT_PAGE_TABLE_POPULATED);
 		goto release;
 	}
 
 	ret = check_stable_address_space(vma->vm_mm);
 	if (ret) {
 		ret = VM_FAULT_FALLBACK;
+		count_vm_event(MCPAGE_ANON_FAULT_INSTABLE_ADDRESS_SPACE);
 		goto release;
 	}
 
@@ -120,6 +123,9 @@ vm_fault_t do_anonymous_mcpages(struct vm_fault *vmf, unsigned int order)
 			break;
 	}
 
+	if (i == nr)
+		count_vm_event(MCPAGE_ANON_FAULT_ALLOC);
+
 	while (i < nr)
 		put_page(&page[i++]);
 
diff --git a/mm/memory.c b/mm/memory.c
index fb7f370f6c67..b3655be849ae 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4079,6 +4079,7 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
 		if (!(ret & VM_FAULT_FALLBACK))
 			return ret;
 
+		count_vm_event(MCPAGE_ANON_FAULT_FALLBACK);
 		ret = 0;
 	}
 
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 1ea6a5ce1c41..c40e33dee1b1 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1367,6 +1367,13 @@ const char * const vmstat_text[] = {
 	"thp_swpout",
 	"thp_swpout_fallback",
 #endif
+#ifdef CONFIG_MCPAGE
+	"mcpage_anon_fault_alloc",
+	"mcpage_anon_fault_fallback",
+	"mcpage_anon_fault_charge_failed",
+	"mcpage_anon_fault_page_table_populated",
+	"mcpage_anon_fault_instable_address_space",
+#endif
 #ifdef CONFIG_MEMORY_BALLOON
 	"balloon_inflate",
 	"balloon_deflate",
-- 
2.30.2