[Gllug] swap over the network

[Kristian Erik Hermansen]

On Jan 23, 2008 4:54 PM, Adrian McMenamin
<adrian at newgolddream.dyndns.info> wrote:
>
> 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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I think my brother knows a bit about this, so I am CC'ing him if he
has any info.  He works at IBRIX, which offers a very advanced
clustering file system...
http://www.ibrix.com/
-- 
Kristian Erik Hermansen
"Know something about everything and everything about something."
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