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

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Message-ID: <20120125065450.GC2005@moon>
Date:	Wed, 25 Jan 2012 10:54:50 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
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 Tue, Jan 24, 2012 at 03:59:41PM -0800, Andrew Morton wrote:
> On Mon, 23 Jan 2012 18:20:39 +0400
> Cyrill Gorcunov <gorcunov@...nvz.org> wrote:
> 
> > We would like to have an ability to restore command line
> > arguments and envirion pointers so the task being restored
> > would print appropriate values in /proc/pid/cmdline and
> > /proc/pid/envirion. The exit_code is needed to restore
> > zombie tasks.
> > 
> 
> Please update Documentation/filesystems/proc.txt.

ok

> > +		(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.
> 
> 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?

	Cyrill
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