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kernel: reduce alignment size of memory hotplug to 128M
After 5.11-rc4, memory hotplug alignment size is reduced to 128M for 4K page. It works better for memory hotplug and nvdimm plug in kata on arm. without this patch, memory hotplug will fail for the current memory hotplug alignment is 1G but the nvdimm size align with 128M in kata. After port it here, we can avoid a fix in qemu side. Note: if you change the page size to other size than 4K, memory hotplug will has no effect. Fixes: #2707 Signed-off-by: Jianyong Wu <jianyong.wu@arm.com>
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Jianyong Wu
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From 5745513881520f48401ac40306ac8cd6ef35beaf Mon Sep 17 00:00:00 2001
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From: Sudarshan Rajagopalan <sudaraja@codeaurora.org>
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Date: Sun, 26 Sep 2021 13:10:41 +0800
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Subject: [PATCH] arm64/sparsemem: reduce SECTION_SIZE_BITS
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memory_block_size_bytes() determines the memory hotplug granularity i.e the
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amount of memory which can be hot added or hot removed from the kernel. The
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generic value here being MIN_MEMORY_BLOCK_SIZE (1UL << SECTION_SIZE_BITS)
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for memory_block_size_bytes() on platforms like arm64 that does not override.
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Current SECTION_SIZE_BITS is 30 i.e 1GB which is large and a reduction here
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increases memory hotplug granularity, thus improving its agility. A reduced
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section size also reduces memory wastage in vmemmmap mapping for sections
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with large memory holes. So we try to set the least section size as possible.
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A section size bits selection must follow:
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(MAX_ORDER - 1 + PAGE_SHIFT) <= SECTION_SIZE_BITS
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CONFIG_FORCE_MAX_ZONEORDER is always defined on arm64 and so just following it
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would help achieve the smallest section size.
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SECTION_SIZE_BITS = (CONFIG_FORCE_MAX_ZONEORDER - 1 + PAGE_SHIFT)
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SECTION_SIZE_BITS = 22 (11 - 1 + 12) i.e 4MB for 4K pages
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SECTION_SIZE_BITS = 24 (11 - 1 + 14) i.e 16MB for 16K pages without THP
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SECTION_SIZE_BITS = 25 (12 - 1 + 14) i.e 32MB for 16K pages with THP
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SECTION_SIZE_BITS = 26 (11 - 1 + 16) i.e 64MB for 64K pages without THP
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SECTION_SIZE_BITS = 29 (14 - 1 + 16) i.e 512MB for 64K pages with THP
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But there are other problems in reducing SECTION_SIZE_BIT. Reducing it by too
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much would over populate /sys/devices/system/memory/ and also consume too many
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page->flags bits in the !vmemmap case. Also section size needs to be multiple
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of 128MB to have PMD based vmemmap mapping with CONFIG_ARM64_4K_PAGES.
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Given these constraints, lets just reduce the section size to 128MB for 4K
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Signed-off-by: Sudarshan Rajagopalan <sudaraja@codeaurora.org>
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Suggested-by: Anshuman Khandual <anshuman.khandual@arm.com>
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Suggested-by: David Hildenbrand <david@redhat.com>
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Cc: Catalin Marinas <catalin.marinas@arm.com>
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Cc: Will Deacon <will@kernel.org>
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Cc: Anshuman Khandual <anshuman.khandual@arm.com>
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Cc: David Hildenbrand <david@redhat.com>
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Cc: Mike Rapoport <rppt@linux.ibm.com>
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Cc: Mark Rutland <mark.rutland@arm.com>
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Cc: Logan Gunthorpe <logang@deltatee.com>
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Cc: Andrew Morton <akpm@linux-foundation.org>
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Cc: Steven Price <steven.price@arm.com>
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Cc: Suren Baghdasaryan <surenb@google.com>
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Reviewed-by: David Hildenbrand <david@redhat.com>
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Acked-by: Mike Rapoport <rppt@linux.ibm.com>
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Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
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Link: https://lore.kernel.org/r/43843c5e092bfe3ec4c41e3c8c78a7ee35b69bb0.1611206601.git.sudaraja@codeaurora.org
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Signed-off-by: Will Deacon <will@kernel.org>
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---
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arch/arm64/include/asm/sparsemem.h | 23 +++++++++++++++++++++--
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1 file changed, 21 insertions(+), 2 deletions(-)
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diff --git a/arch/arm64/include/asm/sparsemem.h b/arch/arm64/include/asm/sparsemem.h
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index 1f43fcc79738..eb4a75d720ed 100644
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--- a/arch/arm64/include/asm/sparsemem.h
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+++ b/arch/arm64/include/asm/sparsemem.h
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@@ -7,7 +7,26 @@
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#ifdef CONFIG_SPARSEMEM
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#define MAX_PHYSMEM_BITS CONFIG_ARM64_PA_BITS
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-#define SECTION_SIZE_BITS 30
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-#endif
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+
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+/*
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+ * Section size must be at least 512MB for 64K base
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+ * page size config. Otherwise it will be less than
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+ * (MAX_ORDER - 1) and the build process will fail.
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+ */
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+#ifdef CONFIG_ARM64_64K_PAGES
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+#define SECTION_SIZE_BITS 29
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+
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+#else
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+
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+/*
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+ * Section size must be at least 128MB for 4K base
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+ * page size config. Otherwise PMD based huge page
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+ * entries could not be created for vmemmap mappings.
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+ * 16K follows 4K for simplicity.
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+ */
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+#define SECTION_SIZE_BITS 27
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+#endif /* CONFIG_ARM64_64K_PAGES */
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+
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+#endif /* CONFIG_SPARSEMEM*/
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#endif
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--
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2.17.1
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