arm64: make ARCH_FORCE_MAX_ORDER selectable

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The other architectures with ARCH_FORCE_MAX_ORDER are selectable,
but not for ARM64, this is to make it selectable on ARM64, which
is useful for user that need to allocate more than 4MB of physically
contiguous memory with 4K pagesize, also bigger on 16K pagesize too, the
max value of MAX_ORDER is calculated bellow,

see include/linux/mmzone.h,

  MAX_ORDER - 1 + PAGE_SHIFT <= SECTION_SIZE_BITS

  so max value of MAX_ORDER = SECTION_SIZE_BITS + 1 - PAGE_SHIFT

    | SECTION_SIZE_BITS |  PAGE_SHIFT  |  max MAX_ORDER  |  default MAX_ORDER |
----+-------------------+--------------+-----------------+--------------------+
4K  |       27          |      12      |     16          |      11            |
16K |       27          |      14      |     14          |      12            |
64K |       29          |      16      |     14          |      14            |
----+-------------------+--------------+-----------------+--------------------+

Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Link: https://lore.kernel.org/r/20230104130000.69806-1-wangkefeng.wang@huawei.com
[catalin.marinas@arm.com: add the calculations as comment to arch/arm64/Kconfig]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

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This commit is contained in:

Kefeng Wang 2023-01-04 21:00:00 +08:00 • committed by Catalin Marinas

parent b7bfaa761d

commit 5a4c2a3140

1 changed files with 14 additions and 1 deletions

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arch/arm64/Kconfig

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