On Tue, Dec 06, 2011 at 11:30:25PM +0800, Christoph Hellwig wrote:

quoted

+	TP_printk("readahead-%s(dev=%d:%d, ino=%lu, "

please don't duplicate the tracepoint name in the output string.
Also don't use braces, as it jsut complicates parsing.

OK. Changed to this format:

        TP_printk("pattern=%s bdi=%s ino=%lu "      
                  "req=%lu+%lu ra=%lu+%d-%d async=%d actual=%d",

quoted

+		  "req=%lu+%lu, ra=%lu+%d-%d, async=%d) = %d",
+			ra_pattern_names[__entry->pattern],

Instead of doing a manual array lookup please use __print_symbolic so
that users of the binary interface (like trace-cmd) also get the
right output.

The patch actually started with 

+#define show_pattern_name(val)                                            \
+       __print_symbolic(val,                                              \
+                       { RA_PATTERN_INITIAL,           "initial"       }, \
+                       { RA_PATTERN_SUBSEQUENT,        "subsequent"    }, \
+                       { RA_PATTERN_CONTEXT,           "context"       }, \
+                       { RA_PATTERN_THRASH,            "thrash"        }, \
+                       { RA_PATTERN_MMAP_AROUND,       "around"        }, \
+                       { RA_PATTERN_FADVISE,           "fadvise"       }, \
+                       { RA_PATTERN_RANDOM,            "random"        }, \
+                       { RA_PATTERN_ALL,               "all"           })

It's then converted to the current form so as to avoid duplicating the
num<>string mapping in two places.

The recently added writeback reason shares the same problem:

        TP_printk("bdi %s: sb_dev %d:%d nr_pages=%ld sync_mode=%d "
                  "kupdate=%d range_cyclic=%d background=%d reason=%s",
...
                  wb_reason_name[__entry->reason]
        )

Fortunately that's newly introduced in 3.2-rc1, so it's still the good
time to fix the writeback traces.

However the problem is, are we going to keep adding duplicate mappings
like this in future?

quoted

--- linux-next.orig/mm/readahead.c	2011-11-29 20:58:53.000000000 +0800
+++ linux-next/mm/readahead.c	2011-11-29 20:59:20.000000000 +0800

@@ -29,6 +29,9 @@ static const char * const ra_pattern_nam
 	[RA_PATTERN_ALL]                = "all",
 };
 
+#define CREATE_TRACE_POINTS
+#include <trace/events/vfs.h>

Maybe we should create a new fs/trace.c just for this instead of stickin
it into the first file that created a tracepoint in the "vfs" namespace.

Yeah, it looks better to move it to a more general place.

Thanks,
Fengguang