Thoughts:
1) I absolutely agree that NFS is far more prominent and useful than any
network block device, at the present time.
2) Nonetheless, swap over NFS is a pretty rare case. I view this work
as interesting, but I really don't see a huge need, for swapping over
NBD or swapping over NFS. I tend to think swapping to a remote resource
starts to approach "migration" rather than merely swapping. Yes, we can
do it... but given the lack of burning need one must examine the price.
3) You note
Swap over network has the problem that the network subsystem does not use fixed
sized allocations, but heavily relies on kmalloc(). This makes mempools
unusable.
True, but IMO there are mitigating factors that should be researched and
taken into account:
a) To give you some net driver background/history, most mainstream net
drivers were coded to allocate RX skbs of size 1538, under the theory
that they would all be allocating out of the same underlying slab cache.
It would not be difficult to update a great many of the [non-jumbo]
cases to create a fixed size allocation pattern.
b) Spare-time experiments and anecdotal evidence points to RX and TX skb
recycling as a potentially valuable area of research. If you are able
to do something like that, then memory suddenly becomes a lot more
bounded and predictable.
So my gut feeling is that taking a hard look at how net drivers function
in the field should give you a lot of good ideas that approach the
shared goal of making network memory allocations more predictable and
bounded.
Jeff
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