This patch is the follow-up from the discussions in the thread [1]. Reducing the section size has the merit of reducing wastage of reserved memory for vmmemmap mappings for sections with large memory holes. Also with smaller section size gives more grunularity and agility for memory hot(un)plugging. But there are also constraints in reducing SECTION_SIZE_BIT: - Should accommodate highest order page for a given config - Should not break PMD mapping in vmemmap for 4K pages - Should not consume too many page->flags bits reducing space for other info This patch uses the suggestions from Anshuman Khandual and David Hildenbrand in thread [1] to set the least possible section size to 128MB for 4K and 16K base page size configs for simplicity, and to 512MB for 64K base page size config. [1] https://lore.kernel.org/lkml/cover.1609895500.git.sudaraja@xxxxxxxxxxxxxx/T/#m8ee60ae69db5e9eb06ca7999c43828d49ccb9626 Sudarshan Rajagopalan (1): arm64/sparsemem: reduce SECTION_SIZE_BITS arch/arm64/include/asm/sparsemem.h | 23 +++++++++++++++++++++-- 1 file changed, 21 insertions(+), 2 deletions(-) -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project
