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SubjectRe: [RFC][PATCH 0/3] TCP/IP Critical socket communication mechanism
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On Thu, 2005-12-15 at 00:21 -0800, David S. Miller wrote:
> From: Sridhar Samudrala <sri@us.ibm.com>
> Date: Wed, 14 Dec 2005 23:37:37 -0800 (PST)
>
> > Instead, you seem to be suggesting in_emergency to be set dynamically
> > when we are about to run out of ATOMIC memory. Is this right?
>
> Not when we run out, but rather when we reach some low water mark, the
> "critical sockets" would still use GFP_ATOMIC memory but only
> "critical sockets" would be allowed to do so.
>
> But even this has faults, consider the IPSEC scenerio I mentioned, and
> this applies to any kind of encapsulation actually, even simple
> tunneling examples can be concocted which make the "critical socket"
> idea fail.
>
> The knee jerk reaction is "mark IPSEC's sockets critical, and mark the
> tunneling allocations critical, and... and..." well you have
> GFP_ATOMIC then my friend.
>
> In short, these "seperate page pool" and "critical socket" ideas do
> not work and we need a different solution, I'm sorry folks spent so
> much time on them, but they are heavily flawed.

maybe it should be approached from the other side; having a way to mark
connections as low priority (say incoming http connections to your
webserver) or as non-critical/expendable would give the "normal"
GFP_ATOMIC ones a better chance in case of overload/DDOS etc. It's not
going to solve the VM deadlock issue wrt iscsi/nfs; however it might be
useful in the "survive slashdot" sense...

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