diff mbox series

[03/14] arm64: reword ARCH_FORCE_MAX_ORDER prompt and help text

Message ID 20230323092156.2545741-4-rppt@kernel.org
State New
Headers show
Series arch,mm: cleanup Kconfig entries for ARCH_FORCE_MAX_ORDER | expand

Commit Message

Mike Rapoport March 23, 2023, 9:21 a.m. UTC 
From: "Mike Rapoport (IBM)" <rppt@kernel.org>

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.

Signed-off-by: Mike Rapoport (IBM) <rppt@kernel.org>
---
 arch/arm64/Kconfig | 25 ++++++++++++-------------
 1 file changed, 12 insertions(+), 13 deletions(-)

Comments

Catalin Marinas March 23, 2023, 10:30 a.m. UTC | #1 
On Thu, Mar 23, 2023 at 11:21:45AM +0200, Mike Rapoport wrote:
> From: "Mike Rapoport (IBM)" <rppt@kernel.org>
> 
> 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.
> 
> Signed-off-by: Mike Rapoport (IBM) <rppt@kernel.org>

Acked-by: Catalin Marinas <catalin.marinas@arm.com>
diff mbox series

Patch

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index bab6483e4317..75af4c329224 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 ARM64_4K_PAGES || ARM64_16K_PAGES
+	int "Order of maximal physically contiguous allocations" if 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
@@ -2298,4 +2298,3 @@  endmenu # "CPU Power Management"
 source "drivers/acpi/Kconfig"
 
 source "arch/arm64/kvm/Kconfig"
-