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 <[email protected]> > Suggested-by: David Hildenbrand <[email protected]> > Cc: Will Deacon <[email protected]> > Cc: Anshuman Khandual <[email protected]> > Cc: Mike Rapoport <[email protected]> > Cc: Mark Rutland <[email protected]> > Cc: Suren Baghdasaryan <[email protected]> > --- > 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
