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Date: Sat, 29 Jun 2013 19:21:13 +0200
From: Olivier Houchard <cognet@ci0.org>
To: Alan Cox <alc@rice.edu>
Subject: Re: generic_bs_map()
Message-ID: <20130629172113.GA90854@ci0.org>
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Cc: "arm@freebsd.org" <arm@freebsd.org>,
 Jeff Roberson <jroberson@jroberson.net>
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On Sat, Jun 29, 2013 at 09:21:30AM -0500, Alan Cox wrote:
> Jeff and I have been looking at the various kmem_alloc() calls
> throughout the kernel, and when we came to generic_bs_map() on arm, I
> was a bit puzzled.  In short, I believe that generic_bs_map() should be
> calling kmem_alloc_nofault() instead of kmem_alloc().  It appears to me
> that generic_bs_map() only wants a virtual address range from kmem_*,
> which is what kmem_alloc_nofault() does.  In contrast, kmem_alloc() also
> allocates and maps physical memory at the returned address range.  In
> the case of generic_bs_map(), allocating and mapping physical memory is
> pointless because generic_bs_map() overwrites those mappings with its
> own.  So, the physical pages allocated by kmem_alloc() are wasted.
> 
> Neither Jeff nor I have arm hardware to verify this change.  Could
> someone here please try it out?
> 
> Thanks,
> Alan
> 

Hmm you have a point, I don't know how we ended up using kmem_alloc() there,
when we rightfully use kmem_alloc_nofault() in pmap_mapdev().
I'll fix this tomorrow if nobody beats me at it.

Regards,

Olivier