Subject: Re: [RFC PATCH 0/9] powerpc/mm: Restructure Linux PTE on Book3S/64 to radix format

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Sun, 21 Feb 2016 13:11:17 +0530

"Aneesh Kumar K.V" <[email-masked]> writes:

> Paul Mackerras <[email-masked]> writes:
>
>> This patch series modifies the Linux PTE format used on 64-bit Book3S
>> processors (i.e. POWER server processors) to make the bits line up
>> with the PTE format used in the radix trees defined in PowerISA v3.0.
>> This will reduce the amount of further change required to make a
>> kernel that can run with either a radix MMU or a hashed page table
>> (HPT) MMU.
>>
>> This also changes the upper levels of the tree to use real addresses
>> rather than kernel virtual addresses - that is, we no longer have the
>> 0xc000... at the top of each PGD/PUD/PMD entry.  I made this change
>> for all 64-bit machines, both embedded and server.
>>
>> The patch series is against v4.5-rc4 plus Aneesh's "powerpc/mm/hash:
>> Clear the invalid slot information correctly" patch.
>>
>> I have compiled this for all the defconfigs in the tree, without
>> error.  I have tested this, with the fixes branch of the powerpc tree
>> merged in, both running bare-metal on a POWER8 and in a KVM guest on
>> that POWER8 system.  In the guest I tested both 4k and 64k configs,
>> with THP enabled; in the host I tested with 64k page size and THP
>> enabled.  All these tests ran fine, including running a KVM guest on
>> the bare-metal system.  So far I have done kernel compiles in a loop
>> as the test, but I plan to run LTP and possibly some other tests.
>>
>> Comments welcome.
>
> I was expecting some complex changes in asm and other part of the code. That
> is one of the reason I was holding of a series like this till I get the
> radix merged. I should have really tried the radix/hash linux page table 
> consolidation to see the impact.

One of the details that i hit last time with _PAGE_PTE was the usage of
@h symbol in asm code. I did a quick look and I guess we are ok. But it
will be good to double check. pmdp_splitting_flush (which got removed)
had usages like %4@h etc

-aneesh