linux-kernel - Re: [PATCH] Add a gfp-translate script to help understand page allocation failure reports

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Date:	Mon, 8 Jun 2009 16:38:27 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Mel Gorman <mel@....ul.ie>
Cc:	riel@...hat.com, penberg@...helsinki.fi,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] Add a gfp-translate script to help understand page
 allocation failure reports

On Mon, 8 Jun 2009 14:29:50 +0100
Mel Gorman <mel@....ul.ie> 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
> 
>   mel@...hina:~/linux-2.6 $ scripts/gfp-translate 0x4020
>   Source: /home/mel/linux-2.6
>   Parsing: 0x4020
>   #define __GFP_HIGH	(0x20)	/* Should access emergency pools? */
>   #define __GFP_COMP	(0x4000) /* Add compound page metadata */
> 
> The script is not a work of art but it has come in handy for me a few times
> so I thought I would share.
> 

hm, OK.  Most of the gfp masks I have to decode are in emails and
bugzilla reports.  I guess I'm different.  Plus I wouldn't trust a tool
run on my machine's kernel tree to correctly interpret a gfp mask from
someone else's kernel of different vintage.

But I can see that it would be useful for someone who's debugging a
locally built kernel.

> diff --git a/scripts/gfp-translate b/scripts/gfp-translate
> new file mode 100755

I don't know how to get patches into Linus's tree with the X bit still
set :(  To avoid solving that problem, maybe Pekka can merge this?

> +# Guess the kernel source directory if it's not set. Preference is in order of
> +# o current directory
> +# o /usr/src/linux
> +if [ "$SOURCE" = "" ]; then
> +	if [ -r "/usr/src/linux/Makefile" ]; then
> +		SOURCE=/usr/src/linux
> +	fi
> +	if [ -r "`pwd`/Makefile" ]; then
> +		SOURCE=`pwd`
> +	fi
> +fi

OK.

> +# Confirm that a source directory exists
> +if [ ! -r "$SOURCE/Makefile" ]; then
> +	die "Could not locate source directory or it is invalid"
> +fi

"kernel source directory".

> +# Confirm that a GFP mask has been specified
> +if [ "$GFPMASK" = "none" ]; then
> +	usage
> +fi
> +
> +# Extract GFP flags from the kernel source
> +TMPFILE=`mktemp -t gfptranslate-XXXXXX` || exit 1
> +grep "^#define __GFP" $SOURCE/include/linux/gfp.h | sed -e 's/(__force gfp_t)//' | sed -e 's/u)/)/' | grep -v GFP_BITS | sed -e 's/)\//) \//' > $TMPFILE
> +
> +# Parse the flags
> +IFS="
> +"
> +echo Source: $SOURCE
> +echo Parsing: $GFPMASK
> +for LINE in `cat $TMPFILE`; do
> +	MASK=`echo $LINE | awk '{print $3}'`
> +	if [ $(($GFPMASK&$MASK)) -ne 0 ]; then
> +		echo $LINE
> +	fi
> +done
> +
> +rm -f $TMPFILE
> +exit 0
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