mm, tracing: improve rss_stat tracepoint message

Adjust the rss_stat tracepoint to print the name of the resident page type
that got updated (e.g. MM_ANONPAGES/MM_FILEPAGES), rather than the numeric
index corresponding to it (the __entry->member value):

Before this patch:
------------------
  rss_stat: mm_id=1216113068 curr=0 member=1 size=28672B
  rss_stat: mm_id=1216113068 curr=0 member=1 size=0B
  rss_stat: mm_id=534402304 curr=1 member=0 size=188416B
  rss_stat: mm_id=534402304 curr=1 member=1 size=40960B

After this patch:
-----------------
  rss_stat: mm_id=1726253524 curr=1 type=MM_ANONPAGES size=40960B
  rss_stat: mm_id=1726253524 curr=1 type=MM_FILEPAGES size=663552B
  rss_stat: mm_id=1726253524 curr=1 type=MM_ANONPAGES size=65536B
  rss_stat: mm_id=1726253524 curr=1 type=MM_FILEPAGES size=647168B

Use TRACE_DEFINE_ENUM()/__print_symbolic() logic to map the enum values to
the strings they represent, so that userspace tools can also parse the raw
data correctly.

Link: https://lkml.kernel.org/r/20210310162305.4862-1-ovidiu.panait@windriver.com
Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
Suggested-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/trace/events/kmem.h

@@ -343,6 +343,26 @@ static unsigned int __maybe_unused mm_ptr_to_hash(const void *ptr)
 #define __PTR_TO_HASHVAL
 #endif
 
+#define TRACE_MM_PAGES		\
+	EM(MM_FILEPAGES)	\
+	EM(MM_ANONPAGES)	\
+	EM(MM_SWAPENTS)		\
+	EMe(MM_SHMEMPAGES)
+
+#undef EM
+#undef EMe
+
+#define EM(a)	TRACE_DEFINE_ENUM(a);
+#define EMe(a)	TRACE_DEFINE_ENUM(a);
+
+TRACE_MM_PAGES
+
+#undef EM
+#undef EMe
+
+#define EM(a)	{ a, #a },
+#define EMe(a)	{ a, #a }
+
 TRACE_EVENT(rss_stat,
 
 	TP_PROTO(struct mm_struct *mm,
@@ -365,10 +385,10 @@ TRACE_EVENT(rss_stat,
 		__entry->size = (count << PAGE_SHIFT);
 	),
 
-	TP_printk("mm_id=%u curr=%d member=%d size=%ldB",
+	TP_printk("mm_id=%u curr=%d type=%s size=%ldB",
 		__entry->mm_id,
 		__entry->curr,
-		__entry->member,
+		__print_symbolic(__entry->member, TRACE_MM_PAGES),
 		__entry->size)
 	);
 #endif /* _TRACE_KMEM_H */