From: "Bob Woodruff" <robert.j.woodruff@intel.com>
To: "'Timur Tabi'" <timur.tabi@ammasso.com>
Cc: "'Andrew Morton'" <akpm@osdl.org>,
       "Davis, Arlin R" <arlin.r.davis@intel.com>, <hch@infradead.org>,
       <linux-kernel@vger.kernel.org>, <openib-general@openib.org>
Subject: RE: [openib-general] Re: [PATCH][RFC][0/4] InfiniBand userspace verbsimplementation
Date: Mon, 25 Apr 2005 16:29:34 -0700
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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 
>because 
>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.

woody

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