arm64: reword ARCH_FORCE_MAX_ORDER prompt and help text

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.

[rppt@kernel.org: change ARCH_FORCE_MAX_ORDER dependencies]
Link: https://lkml.kernel.org/r/20230325060828.2662773-4-rppt@kernel.org
Link: https://lkml.kernel.org/r/20230324052233.2654090-4-rppt@kernel.org
Signed-off-by: Mike Rapoport (IBM) <rppt@kernel.org>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: David Miller <davem@davemloft.net>
Cc: Dinh Nguyen <dinguyen@kernel.org>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Guo Ren <guoren@kernel.org>
Cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Rich Felker <dalias@libc.org>
Cc: "Russell King (Oracle)" <linux@armlinux.org.uk>
Cc: Will Deacon <will@kernel.org>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 7324032..cc11cdc 100644 (file)
--- 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