linux-kernel - Re: [ckrm-tech] [PATCH 0/2] resource control file system

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Message-ID: <20070307175257.GB17151@in.ibm.com>
Date:	Wed, 7 Mar 2007 23:22:57 +0530
From:	Srivatsa Vaddagiri <vatsa@...ibm.com>
To:	"Paul Menage" <menage@...gle.com>
Cc:	ckrm-tech@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	xemul@...ru, dev@...ru, pj@....com, sam@...ain.net,
	ebiederm@...ssion.com, winget@...gle.com,
	containers@...ts.osdl.org, serue@...ibm.com,
	akpm@...ux-foundation.org
Subject: Re: [ckrm-tech] [PATCH 0/2] resource control file system - aka containers on top of nsproxy!

On Wed, Mar 07, 2007 at 09:29:12AM -0800, Paul Menage wrote:
> That seems bad. With the current way you're doing it, if I mount
> hierarchies A and B on /mnt/A and /mnt/B, then initially all tasks are
> in /mnt/A/tasks and /mnt/B/tasks. If I then create /mnt/A/foo and move
> a process into it, that process disappears from /mnt/B/tasks, since
> its nsproxy no longer matches the nsproxy of B's root container. Or am
> I missing something?

I realized that bug as I was doing cpuset conversion.

Basically, we can't use just tsk->nsproxy to find what tasks are in
a directory (/mnt/B for ex). Here's what I was think we should be doing instead:

struct nsproxy *ns;
void *data;

ns = dentry_of(/mnt/B/tasks)->d_parent->d_fsdata;
data = ns->ctlr_data[some subsystem id which is bound in /mnt/B hierarchy]

we now scan tasklist and find a match if:

	tsk->nsproxy->ctlr_data[the above id] == data

(maybe we need to match on all data from all subsystems bound to B)

There is a similar bug in rcfs_rmdir also. We can't just use the nsproxy
pointed to by dentry to know whether the resource objects are free or
not. I am thinking (if at all resource control has to be provided on top
of nsproxy) that we should have a get_res_ns, similar to get_mnt_ns or
get_uts_ns, which will track number of nsproxies pointing to the same
resource object. If we do that, then rmdir() needs to go and check
those resource object's refcounts to see if a dir is in use or not.

-- 
Regards,
vatsa
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