netdev - Re: [PATCH 00/31] Swap over NFS -v20

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Date:	Sat, 10 Oct 2009 23:10:24 +0200
From:	Pavel Machek <pavel@....cz>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Suresh Jayaraman <sjayaraman@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	netdev@...r.kernel.org, Neil Brown <neilb@...e.de>,
	Miklos Szeredi <mszeredi@...e.cz>, Wouter Verhelst <w@...r.be>,
	trond.myklebust@....uio.no
Subject: Re: [PATCH 00/31] Swap over NFS -v20

On Sat 2009-10-10 14:23:41, Peter Zijlstra wrote:
> On Sat, 2009-10-10 at 14:06 +0200, Pavel Machek wrote:
> > Hi!
> > 
> > > > One of them
> > > > would be the whole VM/net work to just make swap over nbd/iscsi safe.
> > > 
> > > Getting those two 'fixed' is going to be tons of interesting work
> > > because they involve interaction with userspace daemons.
> > > 
> > > NBD has fairly simple userspace, but iSCSI has a rather large userspace
> > > footprint and a rather complicated user/kernel interaction which will be
> > > mighty interesting to get allocation safe.
> > > 
> > > Ideally the swap-over-$foo bits have no userspace component.
> > > 
> > > That said, Wouter is the NBD userspace maintainer and has expressed
> > > interest into looking at making that work, but its sure going to be
> > > non-trivial, esp. since exposing PF_MEMALLOC to userspace is a, not over
> > > my dead-bodym like thing.
> > 
> > Well, as long as nbd-server is on separate machine (with real swap),
> > safe swapping over network should be ok, without PF_MEMALLOC for
> > userspace or similar nightmares, right?
> 
> Nope, as soon as the nbd-client looses its connection you're up shit
> creek.

Oops, right. Putting reconnect logic into the kernel would make sense.

I misunderstood your proposal. I thought you'd want to put
nbd-_server_ into the kernel too. I guess we violently agree that
that's unneccessary.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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