On 16 Oct 2024, at 4:14, Ryan Roberts wrote: > On 15/10/2024 18:42, Zi Yan wrote: >> On 14 Oct 2024, at 6:59, Ryan Roberts wrote: >> >>> Introduce a new Kconfig, ARM64_BOOT_TIME_PAGE_SIZE, which can be >>> selected instead of a page size. When selected, the resulting kernel's >>> page size can be configured at boot via the command line. >>> >>> For now, boot-time page size kernels are limited to 48-bit VA, since >>> more work is required to support LPA2. Additionally MMAP_RND_BITS and >>> SECTION_SIZE_BITS are configured for the worst case (64K pages). Future >>> work could be implemented to be able to configure these at boot time for >>> optimial page size-specific values. >>> >>> Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx> >>> --- >> >> <snip> >> >>> >>> @@ -1588,9 +1601,10 @@ config XEN >>> # 4K | 27 | 12 | 15 | 10 | >>> # 16K | 27 | 14 | 13 | 11 | >>> # 64K | 29 | 16 | 13 | 13 | >>> +# BOOT| 29 | 16 (max) | 13 | 13 | >>> config ARCH_FORCE_MAX_ORDER >>> int >>> - default "13" if ARM64_64K_PAGES >>> + default "13" if ARM64_64K_PAGES || ARM64_BOOT_TIME_PAGE_SIZE >>> default "11" if ARM64_16K_PAGES >>> default "10" >>> help >> >> So boot-time page size kernel always has the highest MAX_PAGE_ORDER, which >> means the section size increases for 4KB and 16KB page sizes. Any downside >> for this? > > I guess there is some cost to the buddy when MAX_PAGE_ORDER is larger than it > needs to be - I expect you can explain those details much better than I can. I'm > just setting it to the worst case for now as it was the easiest solution for the > initial series.
