Messages in this thread | | | Date | Wed, 20 Jan 2021 17:49:33 +0000 | From | Will Deacon <> | Subject | Re: [PATCH 1/1] arm64: reduce section size for sparsemem |
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On Fri, Jan 08, 2021 at 03:16:00PM -0800, Sudarshan Rajagopalan wrote: > 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> > --- > 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*/
Please can you repost this in light of the comments from Anshuman?
Thanks,
Will
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