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

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Message-ID: <6599ad830907040910k5c9d720bqafdf596bbc005783@mail.gmail.com>
Date:	Sat, 4 Jul 2009 09:10:58 -0700
From:	Paul Menage <menage@...gle.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.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

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.

Paul
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