Questions about TTM buffer object maping

[Jerome Glisse]

On Thu, Jul 11, 2013 at 2:24 AM, Daniel Vetter <daniel at ffwll.ch> wrote:
> On Wed, Jul 10, 2013 at 09:00:33PM -0400, Jerome Glisse wrote:
>> On Wed, Jul 10, 2013 at 8:27 PM, Jean-Sébastien Pédron
>> <jean-sebastien.pedron at dumbbell.fr> wrote:
>> > Hello,
>> >
>> > I'm trying to understand how TTM buffer object mapping works on Linux, to
>> > make this behave properly on FreeBSD.
>> >
>> > Here's what I think I understand:
>> >
>> > When a buffer object is mmap()'d, ttm_bo_vm_open() is called. When there's a
>> > page fault, the page is looked up and inserted in the VMA using
>> > vm_insert_mixed(). When a buffer object is munmap()'d, ttm_bo_vm_close() is
>> > called, which drops a reference. When the last reference is dropped, the
>> > buffer object is destroyed.
>> >
>> > What's still not clear to me is how munmap() works here. After talking about
>> > this on IRC with some people, I think that unmap_mapping_range() (called by
>> > ttm_bo_unmap_virtual_locked()) is equivalent to calling munmap() from
>> > userland. Is that true?
>>
>> Yes that's true.
>
> Afaik unmap_mapping_range only kills the ptes and doesn't remove the vma.
> So not equivalent to a munmap from userspace. It simply allows us to
> intercept the next access in the page fault handler and move the buffer
> back into place.
> -Daniel

Yes, i was talking from a page point of view, ie page no longer have
mapping and can
be free.

Cheers,
Jerome