diff --git a/tools/packaging/kernel/patches/5.10.x/0001-arm64-sparsemem-reduce-SECTION_SIZE_BITS.patch b/tools/packaging/kernel/patches/5.10.x/0001-arm64-sparsemem-reduce-SECTION_SIZE_BITS.patch new file mode 100644 index 0000000000..3987779164 --- /dev/null +++ b/tools/packaging/kernel/patches/5.10.x/0001-arm64-sparsemem-reduce-SECTION_SIZE_BITS.patch @@ -0,0 +1,94 @@ +From 5745513881520f48401ac40306ac8cd6ef35beaf Mon Sep 17 00:00:00 2001 +From: Sudarshan Rajagopalan +Date: Sun, 26 Sep 2021 13:10:41 +0800 +Subject: [PATCH] arm64/sparsemem: reduce SECTION_SIZE_BITS + +memory_block_size_bytes() determines the memory hotplug granularity i.e the +amount of memory which can be hot added or hot removed from the kernel. The +generic value here being MIN_MEMORY_BLOCK_SIZE (1UL << SECTION_SIZE_BITS) +for memory_block_size_bytes() on platforms like arm64 that does not override. + +Current SECTION_SIZE_BITS is 30 i.e 1GB which is large and a reduction here +increases memory hotplug granularity, thus improving its agility. A reduced +section size also reduces memory wastage in vmemmmap mapping for sections +with large memory holes. So we try to set the least section size as possible. + +A section size bits selection must follow: +(MAX_ORDER - 1 + PAGE_SHIFT) <= SECTION_SIZE_BITS + +CONFIG_FORCE_MAX_ZONEORDER is always defined on arm64 and so just following it +would help achieve the smallest section size. + +SECTION_SIZE_BITS = (CONFIG_FORCE_MAX_ZONEORDER - 1 + PAGE_SHIFT) + +SECTION_SIZE_BITS = 22 (11 - 1 + 12) i.e 4MB for 4K pages +SECTION_SIZE_BITS = 24 (11 - 1 + 14) i.e 16MB for 16K pages without THP +SECTION_SIZE_BITS = 25 (12 - 1 + 14) i.e 32MB for 16K pages with THP +SECTION_SIZE_BITS = 26 (11 - 1 + 16) i.e 64MB for 64K pages without THP +SECTION_SIZE_BITS = 29 (14 - 1 + 16) i.e 512MB for 64K pages with THP + +But there are other problems in reducing SECTION_SIZE_BIT. Reducing it by too +much would over populate /sys/devices/system/memory/ and also consume too many +page->flags bits in the !vmemmap case. Also section size needs to be multiple +of 128MB to have PMD based vmemmap mapping with CONFIG_ARM64_4K_PAGES. + +Given these constraints, lets just reduce the section size to 128MB for 4K + +Signed-off-by: Sudarshan Rajagopalan +Suggested-by: Anshuman Khandual +Suggested-by: David Hildenbrand +Cc: Catalin Marinas +Cc: Will Deacon +Cc: Anshuman Khandual +Cc: David Hildenbrand +Cc: Mike Rapoport +Cc: Mark Rutland +Cc: Logan Gunthorpe +Cc: Andrew Morton +Cc: Steven Price +Cc: Suren Baghdasaryan +Reviewed-by: David Hildenbrand +Acked-by: Mike Rapoport +Reviewed-by: Catalin Marinas +Link: https://lore.kernel.org/r/43843c5e092bfe3ec4c41e3c8c78a7ee35b69bb0.1611206601.git.sudaraja@codeaurora.org +Signed-off-by: Will Deacon +--- + arch/arm64/include/asm/sparsemem.h | 23 +++++++++++++++++++++-- + 1 file changed, 21 insertions(+), 2 deletions(-) + +diff --git a/arch/arm64/include/asm/sparsemem.h b/arch/arm64/include/asm/sparsemem.h +index 1f43fcc79738..eb4a75d720ed 100644 +--- a/arch/arm64/include/asm/sparsemem.h ++++ b/arch/arm64/include/asm/sparsemem.h +@@ -7,7 +7,26 @@ + + #ifdef CONFIG_SPARSEMEM + #define MAX_PHYSMEM_BITS CONFIG_ARM64_PA_BITS +-#define SECTION_SIZE_BITS 30 +-#endif ++ ++/* ++ * Section size must be at least 512MB for 64K base ++ * page size config. Otherwise it will be less than ++ * (MAX_ORDER - 1) and the build process will fail. ++ */ ++#ifdef CONFIG_ARM64_64K_PAGES ++#define SECTION_SIZE_BITS 29 ++ ++#else ++ ++/* ++ * Section size must be at least 128MB for 4K base ++ * page size config. Otherwise PMD based huge page ++ * entries could not be created for vmemmap mappings. ++ * 16K follows 4K for simplicity. ++ */ ++#define SECTION_SIZE_BITS 27 ++#endif /* CONFIG_ARM64_64K_PAGES */ ++ ++#endif /* CONFIG_SPARSEMEM*/ + + #endif +-- +2.17.1 +