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_EL0
bool "Unmap kernel when running in userspace (aka \"KAISER\")" if EXPERT
