[Devel] Re: [RFC][PATCH] Do not set /proc inode->pid for non-pid-related inodes

[Serge E. Hallyn]

Quoting Eric W. Biederman (ebiederm at xmission.com):
> Dave Hansen <hansendc at us.ibm.com> writes:
> 
> > On Mon, 2007-03-26 at 11:12 -0600, Eric W. Biederman wrote:
> >> 
> >> > In (at least one version of) Dave's patches, the /proc your pidns is
> >> > automatically used when you use /proc.  In that case a /proc should
> >> > just go away when the last task goes away, since noone else can use
> >> > that /proc.
> >> 
> >> Unless I am rather confused that does extremely nasty things to
> >> the VFS dentry cache.  Because a dentry can point at one process
> >> one minute and another process the next.  It is doable but only
> >> at the cost of decreased performance.
> >
> > By using, I think Serge meant "mounting".  We're going to statically
> > assign a /proc mount to a namespace when the mount is created, not fudge
> > it around at runtime.
> 
> I think Serge misread that.  He specifically talked about not having
> to remount /proc.  Therefore I believe he understood it did something
> at runtime.

Yes, looks like I misread the code.

I thought a new sb was created automatically if needed.  Going back I
see this is only done at mount time.

> > How does this thrash the dcache?
> 
> Fudging at runtime is horrible.
> 
> Caching the pid_mnt in the pid_namespace appears fine, as long as
> we get the reference counting correct.
> 
> Eric
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