On 12/5/2011 4:02 PM, Andriy Gapon wrote:
on 05/12/2011 19:58 Alan Cox said the following:
On 12/05/2011 07:56, Andriy Gapon wrote:
Pages should be marked busy only for some special occasions, wired pages are not
normally busy; the correct explanation is quite a bit longer than this, the
comment in the code explains VPO_BUSY as "page is in transit". Right now this
flag doesn't seem tom affect vboxdrv code but it may lead to surprises when some
parts of code that are incorrect now are re-implemented properly:
http://article.gmane.org/gmane.os.freebsd.devel.emulation/9297
VM_ALLOC_NOOBJ implies that the returned page does not have VPO_BUSY set. From
the comment at the head of both vm_page_alloc() and vm_page_alloc_contig():
* VM_ALLOC_NOOBJ page is not associated with an object and
* should not have the flag VPO_BUSY set
Ah, oops, forgot about this.
With regard to the message that the above link points to, I suspect that the
introduction of vm_page_alloc_contig() can be used to address the first problem
that you point out. Specifically, one or more OBJT_PHYS vm objects could be
created and passed to vm_map_find() and then vm_page_alloc_contig() could be
used to fill these vm objects with memory.
That's exactly what I was trying to do when I encountered a need for
VM_ALLOC_NOOBJ - my object was not NULL.
Alan, BTW, is it safe to map an OBJT_PHYS object into the kernel_map and into a
user map (or a few of them) at the same time?
Yes, it is.
Alan
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