About pmap_mapdev() & pmap_unmapdev()

Kohji Okuno okuno.kohji at jp.panasonic.com
Sun Oct 5 04:15:16 UTC 2014


> On Sat, Oct 04, 2014 at 08:53:35PM +0900, Kohji Okuno wrote:
>> Hi Konstantin,
>> Thank you for your prompt response.
>> I will test and report from next monday.
>> >> In addtion, I have one question.
>> >> In current and 10-stable, is vm_map_delete() called by kva_free()?
>> > No, kva_free() only releases the vmem backing, leaving the page
>> > tables intact.  This is why I only did the stable/9 patch.
>> Where are PTEs allocated by pmap_mapdev() freed in current and 10-stable?
>> Could you please explain me?
> They are not freed. The removal of the vmem which covers the address
> space managed by corresponding ptes, allows the reuse of both KVA region
> and corresponding PTEs in the tables. The only concern with the resident
> page tables is to avoid two kva_alloc() to step over each other, and
> this is ensured by vmem.

I agree that normal pages are reusable. But, since the pages mapped by
pmap_mapdev() are concerned with the physicall address of device (For
example: video memory), these PTEs aren't reusable, I think.
So, should we free these PTEs by pmap_unmapdev()?

Best regards,
 Kohji Okuno

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