linux-kernel - Re: [PATCH 1/2] Adds a read-only "procs" file similar to "tasks" that shows only unique tgids

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Date:	Mon, 6 Jul 2009 08:53:23 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Paul Menage <menage@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Benjamin Blum <bblum@...gle.com>,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, lizf@...fujitzu.com
Subject: Re: [PATCH 1/2] Adds a read-only "procs" file similar to "tasks"
 that  shows only unique tgids

On Sat, 4 Jul 2009 09:10:58 -0700
Paul Menage <menage@...gle.com> wrote:

> 2009/7/3 KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>:
> > Anyway, above algorithm shows that it's enough to have per-cgroup bitmap
> > (size can be dinamically changed) rather than big table and ugly sort().
> > How about adding per-cgroup taskid bitmap ?
> > clear/set is very easy.
> >
> 
> A per-cgroup bitmap of task ids would mean (assuming that it's
> implemented as a sparse tree like an IDA) that you'd add extra
> allocations and possible failure points in the fork path - right now
> the fork overhead imposed by the cgroups framework itself is just
> linking yourself into your parent's css_set and bumping its refcount.
> I guess there probably are workloads where doing more work at
> fork/exit time and less at "tasks" scan time is a win, but that has to
> be balanced against those where fork/exit performance is more
> critical, and the fact that it would be adding another way that fork
> could fail.
> 
ok.

But "sorting" at procs file seems not sane ;)

-Kame

> Paul
> 

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