svn commit: r309703 - in head/sys: amd64/amd64 arm64/arm64 i386/i386 vm

[Alan Cox]

On 12/08/2016 07:01, Slawa Olhovchenkov wrote:
> On Thu, Dec 08, 2016 at 04:29:29AM +0000, Alan Cox wrote:
>
>> Author: alc
>> Date: Thu Dec  8 04:29:29 2016
>> New Revision: 309703
>> URL: https://svnweb.freebsd.org/changeset/base/309703
>>
>> Log:
>>   Previously, vm_radix_remove() would panic if the radix trie didn't
>>   contain a vm_page_t at the specified index.  However, with this
>>   change, vm_radix_remove() no longer panics.  Instead, it returns NULL
>>   if there is no vm_page_t at the specified index.  Otherwise, it
>>   returns the vm_page_t.  The motivation for this change is that it
>>   simplifies the use of radix tries in the amd64, arm64, and i386 pmap
>>   implementations.  Instead of performing a lookup before every remove,
>>   the pmap can simply perform the remove.
> Is this performance improvement?
>
>

In that it reduces the number of radix trie operations performed by the
pmap, yes.  However, radix tries are only used in the pmap to store page
table pages that were formerly used by now promoted superpages, so the
net effect is going to be small.