[PATCH -V5 17/25] powerpc/THP: Implement transparent hugepages for ppc64

[David Gibson]

On Fri, Apr 12, 2013 at 10:36:58AM +0530, Aneesh Kumar K.V wrote:
> David Gibson <dwg at au1.ibm.com> writes:
> 
> > On Thu, Apr 11, 2013 at 01:10:29PM +0530, Aneesh Kumar K.V wrote:
> >> David Gibson <dwg at au1.ibm.com> writes:
> >> 
> >> > On Thu, Apr 04, 2013 at 11:27:55AM +0530, Aneesh Kumar K.V wrote:
> >> >> From: "Aneesh Kumar K.V" <aneesh.kumar at linux.vnet.ibm.com>
> >> >> 
> >> >> We now have pmd entries covering to 16MB range. To implement THP on powerpc,
> >> >> we double the size of PMD. The second half is used to deposit the pgtable (PTE page).
> >> >> We also use the depoisted PTE page for tracking the HPTE information. The information
> >> >> include [ secondary group | 3 bit hidx | valid ]. We use one byte per each HPTE entry.
> >> >> With 16MB hugepage and 64K HPTE we need 256 entries and with 4K HPTE we need
> >> >> 4096 entries. Both will fit in a 4K PTE page.
> >> >> 
> >> >> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.vnet.ibm.com>
> >> >> ---
> >> >>  arch/powerpc/include/asm/page.h              |    2 +-
> >> >>  arch/powerpc/include/asm/pgtable-ppc64-64k.h |    3 +-
> >> >>  arch/powerpc/include/asm/pgtable-ppc64.h     |    2 +-
> >> >>  arch/powerpc/include/asm/pgtable.h           |  240 ++++++++++++++++++++
> >> >>  arch/powerpc/mm/pgtable.c                    |  314 ++++++++++++++++++++++++++
> >> >>  arch/powerpc/mm/pgtable_64.c                 |   13 ++
> >> >>  arch/powerpc/platforms/Kconfig.cputype       |    1 +
> >> >>  7 files changed, 572 insertions(+), 3 deletions(-)
> >> >> 
> >> >> diff --git a/arch/powerpc/include/asm/page.h b/arch/powerpc/include/asm/page.h
> >> >> index 38e7ff6..b927447 100644
> >> >> --- a/arch/powerpc/include/asm/page.h
> >> >> +++ b/arch/powerpc/include/asm/page.h
> >> >> @@ -40,7 +40,7 @@
> >> >>  #ifdef CONFIG_HUGETLB_PAGE
> >> >>  extern unsigned int HPAGE_SHIFT;
> >> >>  #else
> >> >> -#define HPAGE_SHIFT PAGE_SHIFT
> >> >> +#define HPAGE_SHIFT PMD_SHIFT
> >> >
> >> > That looks like it could break everything except the 64k page size
> >> > 64-bit base.
> >> 
> >> How about 
> >
> > It seems very dubious to me to have transparent hugepages enabled
> > without explicit hugepages in the first place.
> >
> 
> IMHO once we have THP, we will not be using explicit hugepages unless we
> want 16GB pages.

We still can't go breaking the combination in the interim.  Especially
if users are already in the habit of invoking things with
libhugetlbfs.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson
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