Re: [PATCH 1/1] arm64: reduce section size for sparsemem
From: Sudarshan Rajagopalan
Date: Wed Jan 20 2021 - 14:23:31 EST
On 2021-01-20 09:49, Will Deacon wrote:
On Fri, Jan 08, 2021 at 03:16:00PM -0800, Sudarshan Rajagopalan wrote:
Reducing the section size helps reduce wastage of reserved memory
for huge memory holes in sparsemem model. But having a much smaller
section size bits could break PMD mappings for vmemmap and wouldn't
accomodate the highest order page for certain page size granule
configs.
It is determined that SECTION_SIZE_BITS of 27 (128MB) could be ideal
default value for 4K_PAGES that gives least section size without
breaking
PMD based vmemmap mappings. For simplicity, 16K_PAGES could follow the
same as 4K_PAGES. And the least SECTION_SIZE_BITS for 64K_PAGES is 29
that could accomodate MAX_ORDER.
Signed-off-by: Sudarshan Rajagopalan <sudaraja@xxxxxxxxxxxxxx>
Suggested-by: David Hildenbrand <david@xxxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
---
arch/arm64/include/asm/sparsemem.h | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/include/asm/sparsemem.h
b/arch/arm64/include/asm/sparsemem.h
index 1f43fcc79738..ff08ff6b677c 100644
--- a/arch/arm64/include/asm/sparsemem.h
+++ b/arch/arm64/include/asm/sparsemem.h
@@ -7,7 +7,13 @@
#ifdef CONFIG_SPARSEMEM
#define MAX_PHYSMEM_BITS CONFIG_ARM64_PA_BITS
-#define SECTION_SIZE_BITS 30
-#endif
+
+#if defined(CONFIG_ARM64_4K_PAGES) || defined(CONFIG_ARM64_16K_PAGES)
+#define SECTION_SIZE_BITS 27
+#else
+#define SECTION_SIZE_BITS 29
+#endif /* CONFIG_ARM64_4K_PAGES || CONFIG_ARM64_16K_PAGES */
+
+#endif /* CONFIG_SPARSEMEM*/
Please can you repost this in light of the comments from Anshuman?
Thanks,
Will
Sure Will. We were held up with some other critical tasks.. will repost
the patch by EOD after addressing Anshuman's comments.
--
Sudarshan
--
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