[PATCH v6 00/13] Add support for DAX vmemmap optimization for ppc64

[Andrew Morton]

On Wed, 26 Jul 2023 10:59:32 +0530 Aneesh Kumar K V <aneesh.kumar at linux.ibm.com> wrote:

> On 7/26/23 12:59 AM, Andrew Morton wrote:
> > On Tue, 25 Jul 2023 00:37:46 +0530 "Aneesh Kumar K.V" <aneesh.kumar at linux.ibm.com> wrote:
> > 
> >> This patch series implements changes required to support DAX vmemmap
> >> optimization for ppc64.
> > 
> > Do we have any measurements to help us understand the magnitude
> > of this optimization?
> > 
> > And any documentation which helps users understand whether and
> > why they should enable this feature?
> 
> That is memory space optimization due to kernel reusing the tail page struct pages. The details
> of the optimization is documented in patch 11. We document there the impact with both 4k and
> 64K page size.

I suppose that with sufficient arithmetic one could use
Documentation/powerpc/vmemmap_dedup.rst to figure out the bottom-line
savings.

I was more expecting a straightforward statement in the [0/N] overview
to help people understand why they're reading this patchset at all.
Like "saves 5% of total memory on my XXX machine".