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Message-ID: <28c262360906081657o3fb7d825w227aad54f4d0c1af@mail.gmail.com>
Date:	Tue, 9 Jun 2009 08:57:12 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Mel Gorman <mel@....ul.ie>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Rik van Riel <riel@...hat.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH] Add a gfp-translate script to help understand page 
	allocation failure reports

Let's CCed Steven Rostedt :)

On Tue, Jun 9, 2009 at 7:29 AM, Mel Gorman<mel@....ul.ie> wrote:
> On Mon, Jun 08, 2009 at 09:59:06AM -0400, Christoph Hellwig wrote:
>> On Mon, Jun 08, 2009 at 02:29:50PM +0100, Mel Gorman wrote:
>> > The page allocation failure messages include a line that looks like
>> >
>> > page allocation failure. order:1, mode:0x4020
>> >
>> > The mode is easy to translate but irritating for the lazy and a bit error
>> > prone. This patch adds a very simple helper script gfp-translate for the mode:
>> > portion of the page allocation failure messages. An example usage looks like
>>
>> Maybe we just just print the symbolic flags directly?
>
> It'd be nice if it was possible, not ugly and didn't involve declaring
> maps twice.
>
> Even with such hypothetical support, I believe there is scope for having
> the script readily available for use with reports from older kernels,
> particularly distro kernels.
>
>> The even tracer
>> in the for-2.6.23 queue now has a __print_flags helper to translate the
>> bitmask back into symbolic flags, and we even have a kmalloc tracer
>> using it for the GFP flags.  Maybe we should add a printk_flags variant
>> for regular printks and just do the right thing?
>>
>
> The problem I found with a printk_flags variant was that there was no
> buffer for it to easily print to for use with printk("%s"). We can't "see"
> the printk buffer, we can't kmalloc() one and I suspect it's too large to
> place on the stack. What had you in mind?
>
> I haven't looked at the trace implementation before so I have very little
> idea as to how best approach this problem. That didn't stop me attempting a
> hatchet-job on the implementation of printk support for the bitflags->string
> maps declared within ftrace - particularly the GFP flags.
>
> The following patch is what it ended up looking like. I recommend goggles
> because even if we go with printk support, this could be implemented better.
>
> === CUT HERE ===
>
> Add support for %f for the printing of string representation of bit flags
>
> This patch is a prototype to see if the tracing infrastructure used for
> the outputting of symbolic representation of bits set in a flag can be
> reused for printk. With it applied, a page allocation failure report
> looks like
>
> [  171.284889] cat: page allocation failure. order:9, mode:0xd1
> [  171.284948] mode:|GFP_KERNEL|0x1
> [  171.295114] Pid: 2383, comm: cat Not tainted 2.6.30-rc8-tip-02066-g800cfbb-dirty #38
>
> Not-signed-off-yet-by: Mel Gorman <mel@....ul.ie>
>
> diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
> index 5c093ff..8f8e86c 100644
> --- a/include/linux/ftrace_event.h
> +++ b/include/linux/ftrace_event.h
> @@ -16,6 +16,11 @@ struct trace_print_flags {
>        const char              *name;
>  };
>
> +struct trace_printf_spec {
> +       unsigned long                   flags;
> +       struct trace_print_flags        *flag_array;
> +};
> +
>  const char *ftrace_print_flags_seq(struct trace_seq *p, const char *delim,
>                                   unsigned long flags,
>                                   const struct trace_print_flags *flag_array);
> diff --git a/include/trace/events/kmem.h b/include/trace/events/kmem.h
> index 9baba50..e2404ad 100644
> --- a/include/trace/events/kmem.h
> +++ b/include/trace/events/kmem.h
> @@ -17,8 +17,7 @@
>  *
>  * Thus most bits set go first.
>  */
> -#define show_gfp_flags(flags)                                          \
> -       (flags) ? __print_flags(flags, "|",                             \
> +#define gfp_flags_printf_map                                           \
>        {(unsigned long)GFP_HIGHUSER_MOVABLE,   "GFP_HIGHUSER_MOVABLE"}, \
>        {(unsigned long)GFP_HIGHUSER,           "GFP_HIGHUSER"},        \
>        {(unsigned long)GFP_USER,               "GFP_USER"},            \
> @@ -42,6 +41,11 @@
>        {(unsigned long)__GFP_THISNODE,         "GFP_THISNODE"},        \
>        {(unsigned long)__GFP_RECLAIMABLE,      "GFP_RECLAIMABLE"},     \
>        {(unsigned long)__GFP_MOVABLE,          "GFP_MOVABLE"}          \
> +
> +
> +#define show_gfp_flags(flags, map)                                     \
> +       (flags) ? __print_flags(flags, "|",                             \
> +       map                                                             \
>        ) : "GFP_NOWAIT"
>
>  TRACE_EVENT(kmalloc,
> @@ -75,7 +79,7 @@ TRACE_EVENT(kmalloc,
>                __entry->ptr,
>                __entry->bytes_req,
>                __entry->bytes_alloc,
> -               show_gfp_flags(__entry->gfp_flags))
> +               show_gfp_flags(__entry->gfp_flags, gfp_flags_printf_map))
>  );
>
>  TRACE_EVENT(kmem_cache_alloc,
> @@ -109,7 +113,7 @@ TRACE_EVENT(kmem_cache_alloc,
>                __entry->ptr,
>                __entry->bytes_req,
>                __entry->bytes_alloc,
> -               show_gfp_flags(__entry->gfp_flags))
> +               show_gfp_flags(__entry->gfp_flags, gfp_flags_printf_map))
>  );
>
>  TRACE_EVENT(kmalloc_node,
> @@ -146,7 +150,7 @@ TRACE_EVENT(kmalloc_node,
>                __entry->ptr,
>                __entry->bytes_req,
>                __entry->bytes_alloc,
> -               show_gfp_flags(__entry->gfp_flags),
> +               show_gfp_flags(__entry->gfp_flags, gfp_flags_printf_map),
>                __entry->node)
>  );
>
> @@ -184,7 +188,7 @@ TRACE_EVENT(kmem_cache_alloc_node,
>                __entry->ptr,
>                __entry->bytes_req,
>                __entry->bytes_alloc,
> -               show_gfp_flags(__entry->gfp_flags),
> +               show_gfp_flags(__entry->gfp_flags, gfp_flags_printf_map),
>                __entry->node)
>  );
>
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 756ccaf..acb20e0 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -25,6 +25,7 @@
>  #include <linux/kallsyms.h>
>  #include <linux/uaccess.h>
>  #include <linux/ioport.h>
> +#include <linux/ftrace_event.h>
>
>  #include <asm/page.h>          /* for PAGE_SIZE */
>  #include <asm/div64.h>
> @@ -403,6 +404,7 @@ enum format_type {
>        FORMAT_TYPE_CHAR,
>        FORMAT_TYPE_STR,
>        FORMAT_TYPE_PTR,
> +       FORMAT_TYPE_TRACE_FLAGS,
>        FORMAT_TYPE_PERCENT_CHAR,
>        FORMAT_TYPE_INVALID,
>        FORMAT_TYPE_LONG_LONG,
> @@ -574,6 +576,44 @@ static char *string(char *buf, char *end, char *s, struct printf_spec spec)
>        return buf;
>  }
>
> +/*
> + * Support a %f thing storing a struct trace_print_flags
> + */
> +static char *trace_flags(char *buf, char *end,
> +                               struct trace_printf_spec *trace_flags_spec,
> +                               struct printf_spec spec)
> +{
> +       unsigned long mask;
> +       unsigned long flags = trace_flags_spec->flags;
> +       struct trace_print_flags *flag_array = trace_flags_spec->flag_array;
> +       char *str;
> +       char *delim = "|";
> +       char *ret = buf;
> +       int i;
> +
> +       for (i = 0;  flag_array[i].name && flags; i++) {
> +
> +               mask = flag_array[i].mask;
> +               if ((flags & mask) != mask)
> +                       continue;
> +
> +               str = (char *)flag_array[i].name;
> +               flags &= ~mask;
> +               if (ret < end && delim)
> +                       ret = string(ret, end, delim, spec);
> +               ret = string(ret, end, str, spec);
> +       }
> +
> +       if (flags) {
> +               ret = string(ret, end, delim, spec);
> +               spec.flags |= SPECIAL|SMALL;
> +               spec.base = 16;
> +               ret = number(ret, end, flags, spec);
> +       }
> +
> +       return ret;
> +}
> +
>  static char *symbol_string(char *buf, char *end, void *ptr,
>                                struct printf_spec spec, char ext)
>  {
> @@ -888,6 +928,11 @@ qualifier:
>                return fmt - start;
>                /* skip alnum */
>
> +       case 'f':
> +               spec->qualifier = 'l';
> +               spec->type = FORMAT_TYPE_TRACE_FLAGS;
> +               return ++fmt - start;
> +
>        case 'n':
>                spec->type = FORMAT_TYPE_NRCHARS;
>                return ++fmt - start;
> @@ -1058,6 +1103,12 @@ int vsnprintf(char *buf, size_t size, const char *fmt, va_list args)
>                                fmt++;
>                        break;
>
> +               case FORMAT_TYPE_TRACE_FLAGS:
> +                       str = trace_flags(str, end,
> +                               va_arg(args, struct trace_printf_spec *),
> +                               spec);
> +                       break;
> +
>                case FORMAT_TYPE_PERCENT_CHAR:
>                        if (str < end)
>                                *str = '%';
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index ed766b5..714b5c2 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -47,6 +47,7 @@
>  #include <linux/page-isolation.h>
>  #include <linux/page_cgroup.h>
>  #include <linux/debugobjects.h>
> +#include <linux/ftrace_event.h>
>
>  #include <asm/tlbflush.h>
>  #include <asm/div64.h>
> @@ -172,6 +173,11 @@ static void set_pageblock_migratetype(struct page *page, int migratetype)
>                                        PB_migrate, PB_migrate_end);
>  }
>
> +struct trace_print_flags trace_print_flags_gfp[] = {
> +       gfp_flags_printf_map,
> +       { -1, NULL }
> +};
> +
>  #ifdef CONFIG_DEBUG_VM
>  static int page_outside_zone_boundaries(struct zone *zone, struct page *page)
>  {
> @@ -1675,9 +1681,15 @@ nofail_alloc:
>
>  nopage:
>        if (!(gfp_mask & __GFP_NOWARN) && printk_ratelimit()) {
> +               static struct trace_printf_spec gfpmask_printspec;
> +               gfpmask_printspec.flags = gfp_mask;
> +               gfpmask_printspec.flag_array = trace_print_flags_gfp;
> +
>                printk(KERN_WARNING "%s: page allocation failure."
> -                       " order:%d, mode:0x%x\n",
> -                       p->comm, order, gfp_mask);
> +                       " order:%d, mode:0x%x\nmode:%f\n",
> +                       p->comm, order, gfp_mask,
> +                       &gfpmask_printspec);
> +
>                dump_stack();
>                show_mem();
>        }
>
> --
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-- 
Kinds regards,
Minchan Kim
--
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