From owner-freebsd-arm@FreeBSD.ORG  Wed Jan 28 10:37:06 2009
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Date: Wed, 28 Jan 2009 11:37:30 +0100
From: Grzegorz Bernacki <gjb@semihalf.com>
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To: Mark Tinguely <tinguely@casselton.net>, arm@freebsd.org
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Subject: Re: svn commit: r186730 - in head...
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Mark Tinguely wrote:
> Here is the "svn diff" from a week or so ago. The url is below in case
> the inclusion adds some extra characters.
> 
> 	http://www.casselton.net/~tinguely/arm_pmap_unmanage.diff
> 

Mark,

I downloaded your patch and applied it (after a few modification to get rid of compile errors). However, when I boot the board with new code it hangs. The problem is with uma allocator for pv_entries. When there is no more entries available it create new ones. It includes mapping memory into kernel using pmap_qenter. And then recurrence starts, pmap_qenter calls pmap_kenter which tries to allocate pv_entry  and so on. 
I think that pv_entries for pmap_kenter should be allocated from some special pool to avoid this problem. Or some threshold could be set for uma allocator to force allocation of new pv_entries if number of free entries drops below the threshold, but I am not sure if it is possible without extending uma interface.

Grzesiek