On 2023/3/25 14:08, Mike Rapoport wrote:
From: "Mike Rapoport (IBM)" <rppt@xxxxxxxxxx> The prompt and help text of ARCH_FORCE_MAX_ORDER are not even close to describe this configuration option. Update both to actually describe what this option does. Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Reviewed-by: Zi Yan <ziy@xxxxxxxxxx> Signed-off-by: Mike Rapoport (IBM) <rppt@xxxxxxxxxx>
Reviewed-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
--- arch/arm64/Kconfig | 24 ++++++++++++------------ 1 file changed, 12 insertions(+), 12 deletions(-) diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 7324032af859..cc11cdcf5a00 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -1487,24 +1487,24 @@ config XEN # 16K | 27 | 14 | 13 | 11 | # 64K | 29 | 16 | 13 | 13 | config ARCH_FORCE_MAX_ORDER - int "Maximum zone order" if EXPERT && (ARM64_4K_PAGES || ARM64_16K_PAGES) + int "Order of maximal physically contiguous allocations" if EXPERT && (ARM64_4K_PAGES || ARM64_16K_PAGES) default "13" if ARM64_64K_PAGES default "11" if ARM64_16K_PAGES default "10" help - The kernel memory allocator divides physically contiguous memory - blocks into "zones", where each zone is a power of two number of - pages. This option selects the largest power of two that the kernel - keeps in the memory allocator. If you need to allocate very large - blocks of physically contiguous memory, then you may need to - increase this value. + The kernel page allocator limits the size of maximal physically + contiguous allocations. The limit is called MAX_ORDER and it + defines the maximal power of two of number of pages that can be + allocated as a single contiguous block. This option allows + overriding the default setting when ability to allocate very + large blocks of physically contiguous memory is required.- We make sure that we can allocate up to a HugePage size for each configuration.- Hence we have : - MAX_ORDER = PMD_SHIFT - PAGE_SHIFT => PAGE_SHIFT - 3 + The maximal size of allocation cannot exceed the size of the + section, so the value of MAX_ORDER should satisfy- However for 4K, we choose a higher default value, 10 as opposed to 9, giving us- 4M allocations matching the default size used by generic code. + MAX_ORDER + PAGE_SHIFT <= SECTION_SIZE_BITS + + Don't change if unsure.config UNMAP_KERNEL_AT_EL0bool "Unmap kernel when running in userspace (aka \"KAISER\")" if EXPERT
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