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SubjectRe: [PATCH 10/10] mm, treewide: Redefine MAX_ORDER sanely
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On 3/16/23 16:30, Kirill A. Shutemov wrote:
> On Thu, Mar 16, 2023 at 11:15:47AM -0700, Mike Kravetz wrote:
>> On 03/15/23 14:31, Kirill A. Shutemov wrote:
>>> MAX_ORDER currently defined as number of orders page allocator supports:
>>> user can ask buddy allocator for page order between 0 and MAX_ORDER-1.
>>>
>>> This definition is counter-intuitive and lead to number of bugs all over
>>> the kernel.
>>>
>>> Change the definition of MAX_ORDER to be inclusive: the range of orders
>>> user can ask from buddy allocator is 0..MAX_ORDER now.
>>>
>>> --- a/arch/arc/Kconfig
>>> +++ b/arch/arc/Kconfig
>>> @@ -556,7 +556,7 @@ endmenu # "ARC Architecture Configuration"
>>>
>>> config ARCH_FORCE_MAX_ORDER
>>> int "Maximum zone order"
>>> - default "12" if ARC_HUGEPAGE_16M
>>> - default "11"
>>> + default "11" if ARC_HUGEPAGE_16M
>>> + default "10"
>> Is this Kconfig file wrong (off by 1) today? It seems like it wants MAX_ORDER
>> to be sufficiently large to allocate 16M if ARC_HUGEPAGE_16M. So, seems like
>> it should be 13 today?
> +Vineet.
>
> Hm. I think it is okay as long as CONFIG_ARC_PAGE_SIZE_8K=y which is
> default, but breaks for other PAGE_SIZE.
>
> Looks like ARCH_FORCE_MAX_ORDER calculation should involve selected page
> size.

Thats right 8K is default for ARC.

-Vineet

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