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Date:      Wed, 15 Dec 2010 10:26:37 -0800
From:      Julian Elischer <julian@freebsd.org>
To:        "Dr. Baud" <drbaud@yahoo.com>
Cc:        freebsd-hackers@freebsd.org
Subject:   Re: Driver memory allocation
Message-ID:  <4D09085D.7050006@freebsd.org>
In-Reply-To: <66322.83509.qm@web120712.mail.ne1.yahoo.com>
References:  <66322.83509.qm@web120712.mail.ne1.yahoo.com>

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On 12/15/10 4:33 AM, Dr. Baud wrote:
>      Is there a cap on the amount of memory a driver (via bus_dmamem_alloc) can
> allocate, other than the obvious physical memory limit minus the memory already
> allocated?
>
well it has to fit into the kernel virtual space too.
this is quite limited on x86 though  for amd64 it is a lot bigger.

I have seen drivers on amd64 setting asside a couple of GB (but you need
a new kernel that has the kernel virtual space expanded). The kernel can
make use of the direct-map space for driver allocation too.

>      Dr.
>
>
>
>
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