Re: [RFC][PATCH 0/6] Critical Page Pool

From: Sridhar Samudrala
Date: Fri Dec 16 2005 - 00:12:42 EST


Matthew Dobson wrote:

Pavel Machek wrote:


And as you noticed, it does not work for your original usage case,
because reserved memory pool would have to be "sum of all network
interface bandwidths * ammount of time expected to survive without
network" which is way too much.


Well, I never suggested it didn't work for my original usage case. The
discussion we had is that it would be incredibly difficult to 100%
iron-clad guarantee that the pool would NEVER run out of pages. But we can
size the pool, especially given a decent workload approximation, so as to
make failure far less likely.


Perhaps you should add file in Documentation/ explaining it is not
reliable?



That's a good suggestion. I will rework the patch's additions to
Documentation/sysctl/vm.txt to be more clear about exactly what we're
providing.




If you want few emergency pages for some strange hack you are doing
(swapping over network?), just put swap into ramdisk and swapon() it
when you are in emergency, or use memory hotplug and plug few more
gigabytes into your machine. But don't go introducing infrastructure
that _can't_ be used right.


Well, that's basically the point of posting these patches as an RFC. I'm
not quite so delusional as to think they're going to get picked up right
now. I was, however, hoping for feedback to figure out how to design
infrastructure that *can* be used right, as well as trying to find other
potential users of such a feature.


Well, we don't usually take infrastructure that has no in-kernel
users, and example user would indeed be nice.
Pavel



Understood. I certainly wouldn't expect otherwise. I'll see if I can get
Sridhar to post his networking changes that take advantage of this.


I have posted these patches yesterday on lkml and netdev and here is a link to the thread.
http://thread.gmane.org/gmane.linux.kernel/357835
Thanks
Sridhar

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