linux-kernel - Re: [patch 3/4] c/r: procfs: add arg_start/end, env_start/end and exit

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Date:	Tue, 24 Jan 2012 23:12:45 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	Pavel Emelyanov <xemul@...allels.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Kees Cook <keescook@...omium.org>, Tejun Heo <tj@...nel.org>,
	Andrew Vagin <avagin@...nvz.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Vasiliy Kulikov <segoon@...nwall.com>
Subject: Re: [patch 3/4] c/r: procfs: add arg_start/end, env_start/end and
 exit_code members to /proc/$pid/stat

On Wed, 25 Jan 2012 10:54:50 +0400 Cyrill Gorcunov <gorcunov@...il.com> wrote:

> > > +		(mm && permitted) ? mm->start_brk : 0,
> > > +		(mm && permitted) ? mm->arg_start : 0,
> > > +		(mm && permitted) ? mm->arg_end : 0,
> > > +		(mm && permitted) ? mm->env_start : 0,
> > > +		(mm && permitted) ? mm->env_end : 0,
> > > +		task->exit_code);
> > >  	if (mm)
> > >  		mmput(mm);
> > >  	return 0;
> > 
> > /proc/pid/stat is getting out of control.  People are now sending patches
> > because reading from this thing already takes too long.

err, actually, that was /proc/stat/

> > The problem is that if you only want one field, you have to incur the
> > cost of preparing all the fields.  The magnitude of this problem
> > increases exponentially over time!
> > 
> > I'm unsure what to do about it really.  Perhaps add a new
> > /proc/pid/mmstat for MM-specific things.  We could put the above six
> > fields in there, as long as we move quickly.
> > 
> 
> I can add prctl PR_GET_MM with subcodes, since PR_SET_MM is already here
> and wrapped with CHECKPOINT_RESTORE. Would this be better?

mm, not really - /proc is the logical/expected place for it.

I'm thinking that perhaps we should start again with all of this and
export all this information in brand new, well-designed procfs files. 
We'd still maintain /proc/stat and /proc/pid/stat but people should
migrate off them.  Eventually (10 years?) everyone will be setting their
CONFIG_PROC_[PID_]STAT to 'n' and perhaps we can retire the things.

Meanwhile, I suppose you may as well continue to make /proc/pid/stat
even crazier :(  It isn't as bad as /proc/stat!


btw, do we really need to do "(mm && permitted)" so many times?  ie,
can we split that seq_printf up and do

	if (mm && permitted) {
		seq_printf(m + offset, "%lu", mm->start_data);
		...
	} else {
		seq_printf(m + offset, "0 0 0 0 0 0 0 0 0");
	}

?  Although this probably won't help much.
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