svn commit: r233011 - head/sys/powerpc/aim

[Nathan Whitehorn]

On 03/15/12 18:40, Alan Cox wrote:
> On 3/15/2012 5:55 PM, Nathan Whitehorn wrote:
>> On 03/15/12 17:18, Alan Cox wrote:
>>> On 3/15/2012 2:36 PM, Nathan Whitehorn wrote:
>>>> Author: nwhitehorn
>>>> Date: Thu Mar 15 19:36:52 2012
>>>> New Revision: 233011
>>>> URL: http://svn.freebsd.org/changeset/base/233011
>>>>
>>>> Log:
>>>>    Improve algorithm for deciding whether to loop through all 
>>>> process pages
>>>>    or look them up individually in pmap_remove() and apply the same 
>>>> logic
>>>>    in the other ranged operation (pmap_protect). This speeds up make
>>>>    installworld by a factor of 2 on powerpc64.
>>>>
>>>>    MFC after:    1 week
>>>>
>>>> Modified:
>>>>    head/sys/powerpc/aim/mmu_oea64.c
>>>>
>>>
>>> As an additional, related optimization, you should look into 
>>> implementing pmap_remove_pages().
>>>
>>> Alan
>>>
>>
>> Thanks! I didn't know about that one. Is there a reason it isn't 
>> called at the end of vm_pageout_map_deactivate_pages(), which seems 
>> to deactivate all pages with pmap_remove()?
>
> Yes, at least two reasons come to mind.  Some implementations only 
> accept the caller's current pmap as an argument.  Also, there 
> shouldn't be any other threads besides the caller using the pmap.
>
>

OK, makes sense (though the PPC implementation doesn't have the 
needs-to-be-the-current-PMAP restriction). One more question while we're 
discussing this. I looked through the various PMAP functions, and found 
three more that aren't implemented:

- pmap_copy()
   The man page for this one says "Actually implementing it may 
seriously reduce system performance." Is this true? Is there any point 
to implementing it if it would be no faster than repeatedly calling 
pmap_copy_page()?

- pmap_object_init_pt()
   This one looks an important potential optimization.

- pmap_align_superpage()
   PowerPC/AIM mostly only supports superpages in 256 MB regions, where 
all pages within that region must be superpages, and pages not in marked 
regions cannot be. Is there any way to usefully implement this in the 
context of our kernel superpage support?
-Nathan