RE: DMA memory limitation?

From: Christophe Beaumont (
Date: Thu Jul 05 2001 - 12:07:17 EST

> On Thu, 5 Jul 2001, Vasu Varma P V wrote:
> > Hi,
> >
> > Is there any limitation on DMA memory we can allocate using
> > kmalloc(size, GFP_DMA)? I am not able to acquire more than
> > 14MB of the mem using this on my PCI SMP box with 256MB ram.
> > I think there is restriction on ISA boards of 16MB.
> > Can we increase it ?
> >
> > thx,
> > Vasu
> 14MB of DMA(able) memory? Err. I think you are trying to
> do something you would never need to do.
And what is that supposed to be????

I have a piece of pretty well designed hardware here... and my
application requires me to have the PCI board to random access
in master mode a whole lot of memory (anywhere from 128MEGS to
1GIG... and possibly more...) so I really do need BIG DMA buffers
(I don't say huge anymore as one can get 1/2 Gig of RAM for just
over 120 bucks???)...

There is no way I can have the piece of hardware behave in
another fashion... and NO it is NOT broken (when you do BOTH
hardware & software, you know about BOTH limitations... there
are just some cases where you have to face some unique issues).
the mem=1024M works pretty fine once you have figured out how
to handle in a fairly simple way this "reserved" memory...

So please software people... do not blame it all on the
hardware... =)

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