acrn-kernel/arch/arm64/include/asm/sparsemem.h

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/* SPDX-License-Identifier: GPL-2.0-only */
/*
* Copyright (C) 2012 ARM Ltd.
*/
#ifndef __ASM_SPARSEMEM_H
#define __ASM_SPARSEMEM_H
#define MAX_PHYSMEM_BITS CONFIG_ARM64_PA_BITS
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 and 16K base page size configs, and to 512MB for 64K base page size config. Signed-off-by: Sudarshan Rajagopalan <sudaraja@codeaurora.org> Suggested-by: Anshuman Khandual <anshuman.khandual@arm.com> Suggested-by: David Hildenbrand <david@redhat.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will@kernel.org> Cc: Anshuman Khandual <anshuman.khandual@arm.com> Cc: David Hildenbrand <david@redhat.com> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Logan Gunthorpe <logang@deltatee.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Steven Price <steven.price@arm.com> Cc: Suren Baghdasaryan <surenb@google.com> Reviewed-by: David Hildenbrand <david@redhat.com> Acked-by: Mike Rapoport <rppt@linux.ibm.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Link: https://lore.kernel.org/r/43843c5e092bfe3ec4c41e3c8c78a7ee35b69bb0.1611206601.git.sudaraja@codeaurora.org Signed-off-by: Will Deacon <will@kernel.org>
2021-01-21 13:29:13 +08:00
/*
* Section size must be at least 512MB for 64K base
* page size config. Otherwise it will be less than
* MAX_ORDER and the build process will fail.
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 and 16K base page size configs, and to 512MB for 64K base page size config. Signed-off-by: Sudarshan Rajagopalan <sudaraja@codeaurora.org> Suggested-by: Anshuman Khandual <anshuman.khandual@arm.com> Suggested-by: David Hildenbrand <david@redhat.com> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will@kernel.org> Cc: Anshuman Khandual <anshuman.khandual@arm.com> Cc: David Hildenbrand <david@redhat.com> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Logan Gunthorpe <logang@deltatee.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Steven Price <steven.price@arm.com> Cc: Suren Baghdasaryan <surenb@google.com> Reviewed-by: David Hildenbrand <david@redhat.com> Acked-by: Mike Rapoport <rppt@linux.ibm.com> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Link: https://lore.kernel.org/r/43843c5e092bfe3ec4c41e3c8c78a7ee35b69bb0.1611206601.git.sudaraja@codeaurora.org Signed-off-by: Will Deacon <will@kernel.org>
2021-01-21 13:29:13 +08:00
*/
#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