linux-kernel - Re: [RFC/PATCH -v2] Add sysfs control to modify a user's cpu share

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Message-ID: <20071005070117.GB30528@linux.vnet.ibm.com>
Date:	Fri, 5 Oct 2007 12:31:17 +0530
From:	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
To:	Valdis.Kletnieks@...edu
Cc:	Heiko Carstens <heiko.carstens@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	Mike Galbraith <efault@....de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	lkml <linux-kernel@...r.kernel.org>, maneesh@...ux.vnet.ibm.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	Sudhir Kumar <skumar@...ux.vnet.ibm.com>
Subject: Re: [RFC/PATCH -v2] Add sysfs control to modify a user's cpu share

On Thu, Oct 04, 2007 at 05:32:17PM -0400, Valdis.Kletnieks@...edu wrote:
> > Shouldn't that be done via uevents? E.g. UID x gets added to the sysfs tree,
> > generates a uevent and a script then figures out the cpu_share and sets it.
> 
> That would tend to be a tad racy - a site may want to set limits in the
> hypothetical /sys/kernel/uids/NNN before the program has a chance to fork-bomb
> or otherwise make it difficult to set a limitfrom within another userspace

Note that there is a default limit enforced on every new user (1024
value for the user's cpu share). This limit should contain any fork-bomb that
the user may launch immediately.

> process.  It's similar to why you want a process to be launched with all its
> ulimit's set, rather than set them after the fork/exec happens...





-- 
Regards,
vatsa
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