# Re: \[PATCH V2\] mm/ioremap: Probe platform for p4d huge map support

- From: Anshuman Khandual \<hidden\>
- Date: 2019-07-04 15:26:22 
- List: linuxppc-dev
- Page: https://ratatoskr.run/linuxppc-dev/2019/07/6493591
- Thread: https://ratatoskr.run/linux-mm/2019/06/6493521/t.md

```text


On 07/03/2019 04:36 AM, Andrew Morton wrote:
> On Fri, 28 Jun 2019 10:50:31 +0530 Anshuman Khandual [ref] wrote:
> 
>> Finishing up what the commit c2febafc67734a ("mm: convert generic code to
>> 5-level paging") started out while levelling up P4D huge mapping support
>> at par with PUD and PMD. A new arch call back arch_ioremap_p4d_supported()
>> is being added which just maintains status quo (P4D huge map not supported)
>> on x86, arm64 and powerpc.
> 
> Does this have any runtime effects?  If so, what are they and why?  If
> not, what's the actual point?

It just finishes up what the previous commit c2febafc67734a ("mm: convert
generic code to 5-level paging") left off with respect p4d based huge page
enablement for ioremap. When HAVE_ARCH_HUGE_VMAP is enabled its just a simple
check from the arch about the support, hence runtime effects are minimal.
```