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 <sudar...@codeaurora.org> Suggested-by: David Hildenbrand <da...@redhat.com> Cc: Will Deacon <w...@kernel.org> Cc: Anshuman Khandual <anshuman.khand...@arm.com> Cc: Mike Rapoport <r...@linux.ibm.com> Cc: Mark Rutland <mark.rutl...@arm.com> Cc: Suren Baghdasaryan <sur...@google.com> --- arch/arm64/include/asm/sparsemem.h | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/arch/arm64/include/asm/sparsemem.h b/arch/arm64/include/asm/sparsemem.h index 1f43fcc79738..ff08ff6b677c 100644 --- a/arch/arm64/include/asm/sparsemem.h +++ b/arch/arm64/include/asm/sparsemem.h @@ -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 -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project