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 and 16K base page size configs, and to 512MB for 64K base page size config. Signed-off-by: Sudarshan Rajagopalan <sudaraja@xxxxxxxxxxxxxx> Suggested-by: Anshuman Khandual <anshuman.khandual@xxxxxxx> Suggested-by: David Hildenbrand <david@xxxxxxxxxx> Cc: Catalin Marinas <catalin.marinas@xxxxxxx> Cc: Will Deacon <will@xxxxxxxxxx> Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx> Cc: David Hildenbrand <david@xxxxxxxxxx> Cc: Mike Rapoport <rppt@xxxxxxxxxxxxx> Cc: Mark Rutland <mark.rutland@xxxxxxx> Cc: Logan Gunthorpe <logang@xxxxxxxxxxxx> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Steven Price <steven.price@xxxxxxx> Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx> --- 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 -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project
