[Gllug] swap over the network

[Adrian McMenamin]

On Wed, 2008-01-23 at 23:04 +0000, Nix wrote:
> On 23 Jan 2008, Adrian McMenamin stated:
> 
> > On Wed, 2008-01-23 at 20:01 +0000, Nix wrote:
> >
> >> Swapping to block devices that don't require allocations to write to
> >> them works. Swapping to anything else is playing with fire.
> >
> > Just for clarity, do you mean NBD should be okay, anything else is
> > flaky?
> 
> NBD is flaky, because network packet reception requires memory
> allocation. If you're unlucky --- say you've got a lot of sockets open
> receiving data and you get a lot of out-of-sequence packets just when
> you're under heavy memory pressure and looking to swap --- you could
> expect to deadlock, without these patches (which, roughly, provide for
> emergency memory pools for allocations needed to receive only the
> swap-related packets when under memory pressure, and immediately discard
> all packets relating to other TCP streams).

OK. For anyone interested: got NBD up and running (eventually - very
hard to get apt to download these files in the limited memory
available).

Swap partition is being used and it seems to keep stress down, but only
a very little bit - "thrashing" is so great that what you gain in memory
you seem to lose in cycles.

(Not scientific, just my impression)

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