[RFC PATCH 0/7] Remove 4k subpage tracking with hash 64K config

[Paul Mackerras]

On Wed, Oct 21, 2015 at 01:42:26AM +0530, Aneesh Kumar K.V wrote:
> Hi,
> 
> This patch series is on top of the series posted at 
> 
> https://lists.ozlabs.org/pipermail/linuxppc-dev/2015-October/135299.html
> "[PATCH V4 00/31] powerpc/mm: Update page table format for book3s 64". In this
> series we remove 4k subpage tracking with 64K config. Instead we do a hash
> table lookup to get the slot information of 4k hash ptes. This also allow us
> to remove real_pte_t. Side effect of the change is that a specific 4k slot
> lookup can result in multiple H_READ hcalls. But that should only impact
> when we are using 4K subpages which should be rare.
> 
> NOTE: I only tested this on systemsim. Wanted to get this out to get early
> feedback.

I tried this on a quad G5 and it seems to work just fine.  On a kernel
compile test there was very little difference in speed - I measured
about 0.4% slowdown but that may not be statistically significant.
This was with 64k pages configured and THP enabled.

Paul.