RE: [openib-general] Re: [PATCH][RFC][0/4] InfiniBand userspace verbsimplementation

From: Bob Woodruff
Date: Mon Apr 25 2005 - 18:33:57 EST

Timur Tabi wrote,

>Any limit would have to be very high - definitely more than just half.
What if the
>application needs to pin 2GB? The customer is not going to buy 4+ GB of
RAM just
>Linux doesn't like pinning more than half. In an x86-32 system, that would
required >PAE
>support and slow everything down.

>Off the top of my head, I'd say Linux would need to allow all but 512MB to
be pinned. >So
>you have 3GB of RAM, Linux should allow you to pin 2.5GB.

That is why we made it tunable, so that people could decide how to allow.

There is probably a better way to do it than some hard limit, but
that would take a little more understanding of the VM system than we had,
and that is why some of the core kernel folks maybe able to help us come up
with a better solution.


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