[PATCH v5 9/9] powerpc/mm: Enable move pmd/pud

[Andrew Morton]

On Thu, 22 Apr 2021 11:13:23 +0530 "Aneesh Kumar K.V" <aneesh.kumar at linux.ibm.com> wrote:

> mremap HAVE_MOVE_PMD/PUD optimization time comparison for 1GB region:
> 1GB mremap - Source PTE-aligned, Destination PTE-aligned
>   mremap time:      1127034ns
> 1GB mremap - Source PMD-aligned, Destination PMD-aligned
>   mremap time:       508817ns
> 1GB mremap - Source PUD-aligned, Destination PUD-aligned
>   mremap time:        23046ns

Well that's nice.

How significant is this in practice?  How common is it for applications
to successfully align the region?  Do real-world applications actually
benefit from this?

Are there userspace libraries (malloc() etc) which should be reworked
to fully exploit this?