On Tue, Nov 21, 2023 at 09:46:57AM -0800, Linus Torvalds wrote:
> On Tue, 21 Nov 2023 at 04:27, Kirill A. Shutemov
> <kirill.shutemov@xxxxxxxxxxxxxxx> wrote:
> >
> > NR_PAGE_ORDERS defines the number of page orders supported by the page
> > allocator, ranging from 0 to MAX_ORDER, MAX_ORDER + 1 in total.
> >
> > NR_PAGE_ORDERS assists in defining arrays of page orders and allows for
> > more natural iteration over them.
>
> These two patches look much better to me, but I think you missed one area.
>
> Most of the Kconfig changes by commit 23baf831a32c ("mm, treewide:
> redefine MAX_ORDER sanely") should also be basically reverted to use
> this new NR_PAGE_ORDERS.
I am not convinced.
Some architectures make this option user-visible and, in my view, user
cares more about the largest page size buddy allocator can provide than
size of the array inside the allocator.
> IOW, I think the ARCH_FORCE_MAX_ORDER #defines etc should also be done
> in "number of page orders". I suspect from a documentation standpoint
> that also makes more sense in places, eg I think that right now your
> patch says
>
> amount of memory for normal system use. The maximum
> - possible value is MAX_ORDER/2. Setting this parameter
> + possible value is MAX_PAGE_ORDER/2. Setting this
>
> and that's actually nonsensical, because it's NR_PAGE_ORDERS that was
> at least historically the boundary (and historically the one that was
> an even number that can be halved cleanly).
Maybe historically (I didn't check), but not now. It is all over the
place. And it more even in MAX_PAGE_ORDER terms than in NR_PAGE_ORDERS:
arch/arc/Kconfig:config ARCH_FORCE_MAX_ORDER
arch/arc/Kconfig- int "Maximum zone order"
arch/arc/Kconfig- default "11" if ARC_HUGEPAGE_16M
arch/arc/Kconfig- default "10"
--
arch/arm/Kconfig:config ARCH_FORCE_MAX_ORDER
arch/arm/Kconfig- int "Order of maximal physically contiguous allocations"
arch/arm/Kconfig- default "11" if SOC_AM33XX
arch/arm/Kconfig- default "8" if SA1111
arch/arm/Kconfig- default "10"
--
arch/arm64/Kconfig:config ARCH_FORCE_MAX_ORDER
arch/arm64/Kconfig- int
arch/arm64/Kconfig- default "13" if ARM64_64K_PAGES
arch/arm64/Kconfig- default "11" if ARM64_16K_PAGES
arch/arm64/Kconfig- default "10"
--
arch/loongarch/Kconfig:config ARCH_FORCE_MAX_ORDER
arch/loongarch/Kconfig- int "Maximum zone order"
arch/loongarch/Kconfig- default "13" if PAGE_SIZE_64KB
arch/loongarch/Kconfig- default "11" if PAGE_SIZE_16KB
arch/loongarch/Kconfig- default "10"
--
arch/m68k/Kconfig.cpu:config ARCH_FORCE_MAX_ORDER
arch/m68k/Kconfig.cpu- int "Order of maximal physically contiguous allocations" if ADVANCED
arch/m68k/Kconfig.cpu- depends on !SINGLE_MEMORY_CHUNK
arch/m68k/Kconfig.cpu- default "10"
--
arch/mips/Kconfig:config ARCH_FORCE_MAX_ORDER
arch/mips/Kconfig- int "Maximum zone order"
arch/mips/Kconfig- default "13" if MIPS_HUGE_TLB_SUPPORT && PAGE_SIZE_64KB
arch/mips/Kconfig- default "12" if MIPS_HUGE_TLB_SUPPORT && PAGE_SIZE_32KB
arch/mips/Kconfig- default "11" if MIPS_HUGE_TLB_SUPPORT && PAGE_SIZE_16KB
arch/mips/Kconfig- default "10"
--
arch/nios2/Kconfig:config ARCH_FORCE_MAX_ORDER
arch/nios2/Kconfig- int "Order of maximal physically contiguous allocations"
arch/nios2/Kconfig- default "10"
--
arch/powerpc/Kconfig:config ARCH_FORCE_MAX_ORDER
arch/powerpc/Kconfig- int "Order of maximal physically contiguous allocations"
arch/powerpc/Kconfig- range 7 8 if PPC64 && PPC_64K_PAGES
arch/powerpc/Kconfig- default "8" if PPC64 && PPC_64K_PAGES
arch/powerpc/Kconfig- range 12 12 if PPC64 && !PPC_64K_PAGES
arch/powerpc/Kconfig- default "12" if PPC64 && !PPC_64K_PAGES
arch/powerpc/Kconfig- range 8 10 if PPC32 && PPC_16K_PAGES
arch/powerpc/Kconfig- default "8" if PPC32 && PPC_16K_PAGES
arch/powerpc/Kconfig- range 6 10 if PPC32 && PPC_64K_PAGES
arch/powerpc/Kconfig- default "6" if PPC32 && PPC_64K_PAGES
arch/powerpc/Kconfig- range 4 10 if PPC32 && PPC_256K_PAGES
--
arch/sh/mm/Kconfig:config ARCH_FORCE_MAX_ORDER
arch/sh/mm/Kconfig- int "Order of maximal physically contiguous allocations"
arch/sh/mm/Kconfig- default "8" if PAGE_SIZE_16KB
arch/sh/mm/Kconfig- default "6" if PAGE_SIZE_64KB
arch/sh/mm/Kconfig- default "13" if !MMU
arch/sh/mm/Kconfig- default "10"
--
arch/sparc/Kconfig:config ARCH_FORCE_MAX_ORDER
arch/sparc/Kconfig- int "Order of maximal physically contiguous allocations"
arch/sparc/Kconfig- default "12"
--
arch/xtensa/Kconfig:config ARCH_FORCE_MAX_ORDER
arch/xtensa/Kconfig- int "Order of maximal physically contiguous allocations"
arch/xtensa/Kconfig- default "10"
--
Kiryl Shutsemau / Kirill A. Shutemov
