[Gllug] swap over the network

[Nix]

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).

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