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FROMLIST: arm64: reduce section size for sparsemem

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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@codeaurora.org>
Suggested-by: David Hildenbrand <david@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>

Link: https://lore.kernel.org/lkml/15cf9a2359197fee0168f820c5c904650d07939e.1610146597.git.sudaraja@codeaurora.org/
Bug: 175715646
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Change-Id: Iecc0369c595bcabe01182a85a5464c87df36c217
This commit is contained in:
Sudarshan Rajagopalan
2021-01-08 15:16:00 -08:00
committed by Suren Baghdasaryan
parent 1935d6e94b
commit 673e9ab6b6
1 changed files with 8 additions and 2 deletions
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10
arch/arm64/include/asm/sparsemem.h
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@@ -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*/
#endif