netdev - Re: [PATCH 00/13] Swap-over-NBD without deadlocking

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Message-ID: <20110426144635.GK4658@suse.de>
Date:	Tue, 26 Apr 2011 15:46:35 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Linux-MM <linux-mm@...ck.org>,
	Linux-Netdev <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	David Miller <davem@...emloft.net>, Neil Brown <neilb@...e.de>
Subject: Re: [PATCH 00/13] Swap-over-NBD without deadlocking

On Tue, Apr 26, 2011 at 04:23:05PM +0200, Peter Zijlstra wrote:
> On Tue, 2011-04-26 at 08:36 +0100, Mel Gorman wrote:
> > Comments?
> 
> Last time I brought up the whole swap over network bits I was pointed
> towards the generic skb recycling work:
> 
>   http://lwn.net/Articles/332037/
> 
> as a means to pre-allocate memory,

I'd taken note of this to take a much closer look if it turned
out reservations were necessary and to find out what happened with
these patches. So far, bigger reservations have *not* been required
but I agree recycling SKBs may be a better alternative than large
reservations or preallocations if they are necessary.

>  and it was suggested to simply pin
> the few route-cache entries required to route these packets and
> dis-allow swap packets to be fragmented (these last two avoid lots of
> funny allocation cases in the network stack).
> 

I did find that only a few route-cache entries should be required. In
the original patches I worked with, there was a reservation for the
maximum possible number of route-cache entries. I thought this was
overkill and instead reserved 1-per-active-swapfile-backed-by-NFS.

-- 
Mel Gorman
SUSE Labs
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