Re: [PATCH 00/31] powerpc/mm: Update page table format for book3s 64

On Mon, 2015-09-28 at 10:26 +0530, Aneesh Kumar K.V wrote:

Scott Wood [off-list ref] writes:

quoted

On Tue, 2015-09-22 at 12:18 +0530, Aneesh Kumar K.V wrote:

quoted

Scott Wood [off-list ref] writes:

quoted

On Mon, 2015-09-21 at 12:10 +0530, Aneesh Kumar K.V wrote:

quoted

Hi All,

This patch series attempt to update book3s 64 linux page table 
format to
make it more flexible. Our current pte format is very restrictive 
and we
overload multiple pte bits. This is due to the non-availability of 
free 
bits
in pte_t. We use pte_t to track the validity of 4K subpages. This 
patch
series free up pte_t of 11 bits by moving 4K subpage tracking to the
lower half of PTE page. The pte format is updated such that we have 
a
better method for identifying a pte entry at pmd level. This will 
also 
enable
us to implement hugetlb migration(not yet done in this series). 

Before making the changes to the pte format, I am splitting the
pte header definition such that we now have the below layout for 
headers

book3s
   32
     hash.h pgtable.h 
   64
     hash.h  pgtable.h hash-4k.h hash-64k.h
booke
  32
     pgtable.h pte-40x.h pte-44x.h pte-8xx.h pte-fsl-booke.h
  64
    pgtable-4k.h  pgtable-64k.h  pgtable.h

40x and 8xx are not booke.  Is there a better name that can be used 
for 
this 
directory?  Maybe "nohash", similar to arch/powerpc/mm/tlb_nohash.c?

I looked at Documentation/powerpc/cpu_families.txt to name the headers.
It lists then below booke.

It lists 40x as booke (there was some question about that when 
cpu_families.txt was added...  I guess you could call it "proto-booke", 
though it doesn't use CONFIG_BOOKE in Linux), but 8xx is in its own 
category.

In any case, "nohash" is the term used elsewhere.

How about using swtlb ? (nohash always confused me, It would be nice to
be explict and us software tlb ?)

I'd prefer nohash.  Besides being existing practice (what's confusing about 
it?), e6500 is nohash but has a partial hw tlb, and 603 is considered hash 
despite having a software-loaded tlb.

-Scott