Re: [PATCH] ipc/shm.c: add RSS and swap size information to /proc/sysvipc/shm

[Andrew Morton <akpm@linux-foundation.org>]

On Wed, 11 Aug 2010 22:13:45 +0200
Helge Deller <deller@gmx.de> wrote:

> The kernel currently provides no functionality to analyze the RSS
> and swap space usage of each individual sysvipc shared memory segment.
> 
> This patch add this info for each existing shm segment by extending
> the output of /proc/sysvipc/shm by two columns for RSS and swap.
> 
> Since shmctl(SHM_INFO) already provides a similiar calculation (it
> currently sums up all RSS/swap info for all segments), I did split
> out a static function which is now used by the /proc/sysvipc/shm 
> output and shmctl(SHM_INFO).
> 

I suppose that could be useful, although it would be most interesting
to hear why _you_ consider it useful?

But is it useful enough to risk breaking existing code which parses
that file?  The risk is not great, but it's there.

> 
> ---
> 
>  shm.c |   63 ++++++++++++++++++++++++++++++++++++++++++---------------------
>  1 file changed, 42 insertions(+), 21 deletions(-)
> 
> 
> diff --git a/ipc/shm.c b/ipc/shm.c
> --- a/ipc/shm.c
> +++ b/ipc/shm.c
> @@ -108,7 +108,11 @@ void __init shm_init (void)
>  {
>  	shm_init_ns(&init_ipc_ns);
>  	ipc_init_proc_interface("sysvipc/shm",
> -				"       key      shmid perms       size  cpid  lpid nattch   uid   gid  cuid  cgid      atime      dtime      ctime\n",
> +#if BITS_PER_LONG <= 32
> +				"       key      shmid perms       size  cpid  lpid nattch   uid   gid  cuid  cgid      atime      dtime      ctime        RSS       swap\n",
> +#else
> +				"       key      shmid perms                  size  cpid  lpid nattch   uid   gid  cuid  cgid      atime      dtime      ctime                   RSS                  swap\n",

This adds 11 new spaces between "perms" and "size", only on 64-bit
machines.  That was unchangelogged and adds another (smaller) risk of
breaking things.  Please explain.

This interface is really old and crufty and horrid, but I guess that
there's not a lot we can do about that :(