Date: Thu, 10 Dec 2015 11:59:44 +0900
From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Minchan Kim <minchan@kernel.org>, Sasha Levin <sasha.levin@oracle.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Mel Gorman <mgorman@suse.de>, Michal Hocko <mhocko@suse.cz>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH v2 1/3] mm, printk: introduce new format string for flags
Message-ID: <20151210025944.GB17967@js1304-P5Q-DELUXE>
References: <87io4hi06n.fsf@rasmusvillemoes.dk>
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Ccing, Steven to ask trace-cmd problem.

On Fri, Dec 04, 2015 at 04:16:33PM +0100, Vlastimil Babka wrote:
> In mm we use several kinds of flags bitfields that are sometimes printed for
> debugging purposes, or exported to userspace via sysfs. To make them easier to
> interpret independently on kernel version and config, we want to dump also the
> symbolic flag names. So far this has been done with repeated calls to
> pr_cont(), which is unreliable on SMP, and not usable for e.g. sysfs export.
> 
> To get a more reliable and universal solution, this patch extends printk()
> format string for pointers to handle the page flags (%pgp), gfp_flags (%pgg)
> and vma flags (%pgv). Existing users of dump_flag_names() are converted and
> simplified.
> 
> It would be possible to pass flags by value instead of pointer, but the %p
> format string for pointers already has extensions for various kernel
> structures, so it's a good fit, and the extra indirection in a non-critical
> path is negligible.

I'd like to use %pgp in tracepoint output. It works well when I do
'cat /sys/kernel/debug/tracing/trace' but not works well when I do
'./trace-cmd report'. It prints following error log.

  [page_ref:page_ref_unfreeze] bad op token &
  [page_ref:page_ref_set] bad op token &
  [page_ref:page_ref_mod_unless] bad op token &
  [page_ref:page_ref_mod_and_test] bad op token &
  [page_ref:page_ref_mod_and_return] bad op token &
  [page_ref:page_ref_mod] bad op token &
  [page_ref:page_ref_freeze] bad op token &

Following is the format I used.

TP_printk("pfn=0x%lx flags=%pgp count=%d mapcount=%d mapping=%p mt=%d val=%d ret=%d",
                __entry->pfn, &__entry->flags, __entry->count,
                __entry->mapcount, __entry->mapping, __entry->mt,
                __entry->val, __entry->ret)

Could it be solved by 'trace-cmd' itself?
Or it's better to pass flags by value?
Or should I use something like show_gfp_flags()?

Thanks.
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