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. > > Is there any plan (not in this patchset) to support boot-time MAX_PAGE_ORDER > to keep section size the same? Yes absolutely. I should have documented MAX_PAGE_ORDER in the commit log along with the comments for MMAP_RND_BITS and SECTION_SIZE_BITS - that was an oversight and I'll fix it in the next version. I plan to look at making all 3 values boot-time configurable in future (although I have no idea at this point how involved that will be). Thanks, Ryan > > Best Regards, > Yan, Zi
