mm: vmalloc: add free_vmap_area_noflush trace event

This event is used in order to validate/debug a start address of freed VA,
number of currently outstanding and maximum allowed areas.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Uladzislau Rezki (Sony) <[e-mail]>
Reviewed-by: Steven Rostedt (Google) <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
Cc: Matthew Wilcox (Oracle) <[e-mail]>
Cc: Nicholas Piggin <[e-mail]>
Cc: Oleksiy Avramchenko <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

include/trace/events/vmalloc.h

···
 		__entry->start, __entry->end, __entry->npurged)
 );
 
+/**
+ * free_vmap_area_noflush - called when a vmap area is freed
+ * @va_start:		a start address of VA
+ * @nr_lazy:		number of current lazy pages
+ * @nr_lazy_max:	number of maximum lazy pages
+ *
+ * This event is used for a debug purpose. It gives some
+ * indication about a VA that is released, number of current
+ * outstanding areas and a maximum allowed threshold before
+ * dropping all of them.
+ */
+TRACE_EVENT(free_vmap_area_noflush,
+
+	TP_PROTO(unsigned long va_start, unsigned long nr_lazy,
+		unsigned long nr_lazy_max),
+
+	TP_ARGS(va_start, nr_lazy, nr_lazy_max),
+
+	TP_STRUCT__entry(
+		__field(unsigned long, va_start)
+		__field(unsigned long, nr_lazy)
+		__field(unsigned long, nr_lazy_max)
+	),
+
+	TP_fast_assign(
+		__entry->va_start = va_start;
+		__entry->nr_lazy = nr_lazy;
+		__entry->nr_lazy_max = nr_lazy_max;
+	),
+
+	TP_printk("va_start=0x%lx nr_lazy=%lu nr_lazy_max=%lu",
+		__entry->va_start, __entry->nr_lazy, __entry->nr_lazy_max)
+);
+
 #endif /*  _TRACE_VMALLOC_H */
 
 /* This part must be outside protection */