linux-kernel - Re: [rfc 2/3] fs, proc: Introduce the Children: line in /proc/<pid>/status

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Date:	Fri, 02 Dec 2011 18:37:10 +0400
From:	Pavel Emelyanov <xemul@...allels.com>
To:	Pedro Alves <pedro@...esourcery.com>
CC:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Cyrill Gorcunov <gorcunov@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>, Andrew Vagin <avagin@...nvz.org>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Vasiliy Kulikov <segoon@...nwall.com>
Subject: Re: [rfc 2/3] fs, proc: Introduce the Children: line in /proc/<pid>/status

On 12/02/2011 06:25 PM, Pedro Alves wrote:
> On Friday 02 December 2011 14:17:08, Pavel Emelyanov wrote:
> 
>> O_O   OK, I was wrong, they do live there. But I consider this as bug.
> 
> You can't change that.  It'd break current gdb at least.

OMG!

>> I.e. each task will be shown multiple times, which is not very fun, but memory exhaustive from my POV.
> 
> Now that is a good argument against hard linking.  But not if you make
> the entries under children/ symlinks.  Then find doesn't recurse.  And
> then 
> 
> $ find -L /proc/PID/
> 
> does recurse and give you the whole tree.  Which I'd say is
> actually useful...

It is useful, but the /proc/pid/children file solves the same problem in a much
more simple way. The memory usage by proc (one file vs one dir and a set of files)
is less and time to lookup a child is also less (read + lookup vs readdir + lookup 
(symlink itself) + lookup (symlink resolve)).

Yes, it doesn't allow you to have fun with find, but frankly, do you really need
this? Even if we're talking about gdb -- reading /proc/pid/children is not harder
and not easier than readdir-ing it.

IOW - what's the real benefit of a directory with symlinks against a file except
for a fun?

Thanks,
Pavel
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