Re: CVS commit: src/sys/uvm

[Matt Thomas <matt%3am-software.com@localhost>]

On Dec 6, 2010, at 8:19 AM, Masao Uebayashi wrote:

> On Thu, Nov 25, 2010 at 11:32:39PM +0000, YAMAMOTO Takashi wrote:
>> [ adding cc: tech-kern@ ]
> 
> The basic idea is straightforward; always allocate vm_physseg for
> memories/devices.  If a vm_physseg is used as general purpose
> memory, you allocate vm_page[] (as vm_physseg::pgs).  If it's
> potentially mapped as cached, you allocate pvh (as vm_physseg:pvh).

Ewww.  How p->v is managed needs to be kept out of the MI code.
There can be a common implementation of it for use by MD code but
that isn't the same as MI.

> Keep vm_physseg * + off_t array on stack.  If UVM objects uses
> vm_page (e.g. vnode), its pager looks up vm_page -> vm_physseg *
> + off_t *once* and cache it on stack.

off_t is not the right type.  psize_t would be more accurate.

>> any valid paddr_t value will belong to exactly one vm_phsseg?
> 
> That's the idea.  This would clarify mem(4) backend too.
> 
> Note that allocating vm_physseg for device segments is cheap.

that's depends on how much more expensive finding physseg gets.