kernel pages superpage promotion/demotion

[suresh gumpula]

Thanks a lot for quick reply Alan.
The super page promotion/demotion  of kernel allocations is done in  9.1
also  I assume .  Please confirm.

Regarding write protection,  I am trying to chase a corruption of uma zone
allocation,  so I was looking at pmap_protect(9).
And thinking of using something like  pmap_protect(kernel_pmap, sva , eva,
VMPROT_READ);  to write protect  sva to eva of a zone allocation return
address.
So  can  pmap_protect(9) be  used for this purpose ?


Thanks
Suresh


On Mon, Oct 12, 2015 at 6:43 PM, Alan Cox <alan.l.cox at gmail.com> wrote:

>
>
> On Mon, Oct 12, 2015 at 3:11 PM, suresh gumpula <gsuryacse7k at gmail.com>
> wrote:
>
>> Hi,
>>       I understand that user space VM map pages dynamically
>> promoted/demoted to super page
>>   if the kernel thinks that it gains the performance.
>>         The question is  , does this apply to kernel map pages too ?
>>
>>
>
> Yes, it applies to memory allocated for UMA zones, malloc(9), and
> contigmalloc(9).
>
>
>
>> And is it possible to write protect kernel address space VA with
>>  pmap_protect(9).   Since the protection is per 4k page,  I see this
>> routine tries to demote to 4k page.
>> Or this is only for user space maps to support  mprotect(2) and gdb
>> watchpoints.
>> Do we have any other API to write protect kernel addresses which come from
>> UMA zone allocations ?
>>
>>
>
> No.
>
> Can you please try to describe what are you trying to do at a higher
> level?
>