Re: [PATCH v3 2/2] powerpc/mm/hugetlb: Add support for 1G huge pages

On Thursday 18 May 2017 10:51 AM, Michael Ellerman wrote:

"Aneesh Kumar K.V" [off-list ref] writes:

quoted

POWER9 supports hugepages of size 2M and 1G in radix MMU mode. This patch
enables the usage of 1G page size for hugetlbfs. This also update the helper
such we can do 1G page allocation at runtime.

We still don't enable 1G page size on DD1 version. This is to avoid doing
workaround mentioned in commit: 6d3a0379ebdc8 (powerpc/mm: Add
radix__tlb_flush_pte_p9_dd1()

Signed-off-by: Aneesh Kumar K.V <redacted>
---
  arch/powerpc/include/asm/book3s/64/hugetlb.h | 10 ++++++++++
  arch/powerpc/mm/hugetlbpage.c                |  7 +++++--
  arch/powerpc/platforms/Kconfig.cputype       |  1 +
  3 files changed, 16 insertions(+), 2 deletions(-)

I think this patch is OK, but it's very confusing because it doesn't
mention that it's only talking about *generic* gigantic page support.

What you mean by generic gigantic page ? what is supported here is the 
gigantic page with size 1G alone ?

We have existing support for gigantic pages on powerpc, on several
platforms. This patch appears to break that, but I think doesn't in
practice?

What is broken ?

So can you make it a bit clearer in the commit message, and the code,
that this is only about enabling the generic gigantic page support, and
is unrelated to the arch-specific gigantic page support.

cheers

quoted

diff --git a/arch/powerpc/include/asm/book3s/64/hugetlb.h b/arch/powerpc/include/asm/book3s/64/hugetlb.h
index 6666cd366596..5c28bd6f2ae1 100644
--- a/arch/powerpc/include/asm/book3s/64/hugetlb.h
+++ b/arch/powerpc/include/asm/book3s/64/hugetlb.h

@@ -50,4 +50,14 @@ static inline pte_t arch_make_huge_pte(pte_t entry, struct vm_area_struct *vma,
  	else
  		return entry;
  }
+
+#ifdef CONFIG_ARCH_HAS_GIGANTIC_PAGE
+static inline bool gigantic_page_supported(void)
+{
+	if (radix_enabled())
+		return true;
+	return false;
+}
+#endif
+
  #endif

diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
index a4f33de4008e..80f6d2ed551a 100644
--- a/arch/powerpc/mm/hugetlbpage.c
+++ b/arch/powerpc/mm/hugetlbpage.c

@@ -763,8 +763,11 @@ static int __init add_huge_page_size(unsigned long long size)
  	 * Hash: 16M and 16G
  	 */
  	if (radix_enabled()) {
-		if (mmu_psize != MMU_PAGE_2M)
-			return -EINVAL;
+		if (mmu_psize != MMU_PAGE_2M) {
+			if (cpu_has_feature(CPU_FTR_POWER9_DD1) ||
+			    (mmu_psize != MMU_PAGE_1G))
+				return -EINVAL;
+		}
  	} else {
  		if (mmu_psize != MMU_PAGE_16M && mmu_psize != MMU_PAGE_16G)
  			return -EINVAL;

diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
index 684e886eaae4..b76ef6637016 100644
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype

@@ -344,6 +344,7 @@ config PPC_STD_MMU_64
  config PPC_RADIX_MMU
  	bool "Radix MMU Support"
  	depends on PPC_BOOK3S_64
+	select ARCH_HAS_GIGANTIC_PAGE if (MEMORY_ISOLATION && COMPACTION) || CMA
  	default y
  	help
  	  Enable support for the Power ISA 3.0 Radix style MMU. Currently this

-- 
2.7.4