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SubjectRe: [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@csn.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@machina:~/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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