mm: introduce per-VMA lock statistics

Add a new CONFIG_PER_VMA_LOCK_STATS config option to dump extra statistics
about handling page fault under VMA lock.

Link: https://lkml.kernel.org/r/20230227173632.3292573-29-surenb@google.comSigned-off-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/vm_event_item.h

@@ -149,6 +149,12 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
 #ifdef CONFIG_X86
 		DIRECT_MAP_LEVEL2_SPLIT,
 		DIRECT_MAP_LEVEL3_SPLIT,
+#endif
+#ifdef CONFIG_PER_VMA_LOCK_STATS
+		VMA_LOCK_SUCCESS,
+		VMA_LOCK_ABORT,
+		VMA_LOCK_RETRY,
+		VMA_LOCK_MISS,
 #endif
 		NR_VM_EVENT_ITEMS
 };

include/linux/vmstat.h

@@ -125,6 +125,12 @@ static inline void vm_events_fold_cpu(int cpu)
 #define count_vm_tlb_events(x, y) do { (void)(y); } while (0)
 #endif
 
+#ifdef CONFIG_PER_VMA_LOCK_STATS
+#define count_vm_vma_lock_event(x) count_vm_event(x)
+#else
+#define count_vm_vma_lock_event(x) do {} while (0)
+#endif
+
 #define __count_zid_vm_events(item, zid, delta) \
 	__count_vm_events(item##_NORMAL - ZONE_NORMAL + zid, delta)
 

mm/Kconfig.debug

@@ -279,3 +279,9 @@ config DEBUG_KMEMLEAK_AUTO_SCAN
 
 	  If unsure, say Y.
 
+config PER_VMA_LOCK_STATS
+	bool "Statistics for per-vma locks"
+	depends on PER_VMA_LOCK
+	default y
+	help
+	  Statistics for per-vma locks.

mm/memory.c

@@ -5284,6 +5284,7 @@ struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm,
 	/* Check if the VMA got isolated after we found it */
 	if (vma->detached) {
 		vma_end_read(vma);
+		count_vm_vma_lock_event(VMA_LOCK_MISS);
 		/* The area was replaced with another one */
 		goto retry;
 	}
@@ -5292,6 +5293,7 @@ struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm,
 	return vma;
 inval:
 	rcu_read_unlock();
+	count_vm_vma_lock_event(VMA_LOCK_ABORT);
 	return NULL;
 }
 #endif /* CONFIG_PER_VMA_LOCK */

mm/vmstat.c

@@ -1399,6 +1399,12 @@ const char * const vmstat_text[] = {
 	"direct_map_level2_splits",
 	"direct_map_level3_splits",
 #endif
+#ifdef CONFIG_PER_VMA_LOCK_STATS
+	"vma_lock_success",
+	"vma_lock_abort",
+	"vma_lock_retry",
+	"vma_lock_miss",
+#endif
 #endif /* CONFIG_VM_EVENT_COUNTERS || CONFIG_MEMCG */
 };
 #endif /* CONFIG_PROC_FS || CONFIG_SYSFS || CONFIG_NUMA || CONFIG_MEMCG */