linux-kernel - Re: Union mount and overlayfs bake off?

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Message-ID: <87vcvnpjxw.fsf@tucsk.pomaz.szeredi.hu>
Date:	Thu, 30 Jun 2011 14:44:59 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	David Howells <dhowells@...hat.com>
Cc:	Ric Wheeler <ricwheeler@...il.com>,
	Michal Suchanek <hramrach@...trum.cz>,
	Alexander Viro <aviro@...hat.com>, Ian Kent <ikent@...hat.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jeff Moyer <jmoyer@...hat.com>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: Union mount and overlayfs bake off?

David Howells <dhowells@...hat.com> writes:

> I've been dealing with some of Al's issues with the unionmount
> patches, but I know he's got more - I just can't remember them all.

A couple of questions I have:

1) What happens to the union in a cloned namespace (CLONE_NEWNS)?

2) What's the overhead for non-unioned filesystems if CONFIG_UNION_MOUNTS
is enabled?  Does it show up in any microbenchmarks?

3) Is there a future strategy for making atomic operations really atomic?
E.g. what happens if power is lost in the middle of a copy-up?  Or if
whiteout of source fails after a successful rename()?

4) Have you looked at overlayfs?  Do you have any thoughts about the
relative merrits of each solution?

Thanks,
Miklos
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