Re: [RFC][PATCH 0/9] Network receive deadlock prevention for NBD

From: Evgeniy Polyakov
Date: Thu Aug 17 2006 - 14:53:41 EST

On Thu, Aug 17, 2006 at 11:01:52AM -0700, Daniel Phillips (phillips@xxxxxxxxxx) wrote:
> *** The system is not OOM, it is in reclaim, a transient condition ***

It does not matter how condition when not every user can get memory is
called. And actually no one can know in advance how long it will be.

> Which Peter already told you! Please, let's get our facts straight,
> then we can look intelligently at whether your work is appropriate to
> solve the block IO network starvation problem that Peter and I are
> working on.

I got openssh as example of situation when system does not know in
advance, what sockets must be marked as critical.
OpenSSH works with network and unix sockets in parallel, so you need to
hack openssh code to be able to allow it to use reserve when there is
not enough memory. Actually all sockets must be able to get data, since
kernel can not diffirentiate between telnetd and a process which will
receive an ack for swapped page or other significant information.
So network must behave separately from main allocator in that period of
time, but since it is possible that reserve can be not filled or has not
enough space or something other, it must be preallocated in far advance
and should be quite big, but then why netwrok should use it at all, when
being separated from main allocations solves the problem?

I do not argue that your approach is bad or does not solve the problem,
I'm just trying to show that further evolution of that idea eventually
ends up in separated allocator (as long as all most robust systems
separate operations), which can improve things in a lot of other sides

> Regards,
> Daniel

Evgeniy Polyakov
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