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CONFIG_ARCH_FORCE_MAX_ORDER: Order of maximal physically contiguous allocations

General informations

The Linux kernel configuration item CONFIG_ARCH_FORCE_MAX_ORDER has multiple definitions:

Order of maximal physically contiguous allocations found in arch/xtensa/Kconfig

The configuration item CONFIG_ARCH_FORCE_MAX_ORDER:

Help text

The kernel page allocator limits the size of maximal physically contiguous allocations. The limit is called MAX_PAGE_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.

Don't change if unsure.

Order of maximal physically contiguous allocations found in arch/sparc/Kconfig

The configuration item CONFIG_ARCH_FORCE_MAX_ORDER:

Help text

The kernel page allocator limits the size of maximal physically contiguous allocations. The limit is called MAX_PAGE_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.

Don't change if unsure.

Order of maximal physically contiguous allocations found in arch/sh/mm/Kconfig

The configuration item CONFIG_ARCH_FORCE_MAX_ORDER:

Help text

The kernel page allocator limits the size of maximal physically contiguous allocations. The limit is called MAX_PAGE:_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.

The page size is not necessarily 4KB. Keep this in mind when choosing a value for this option.

Don't change if unsure.

Order of maximal physically contiguous allocations found in arch/powerpc/Kconfig

The configuration item CONFIG_ARCH_FORCE_MAX_ORDER:

Help text

The kernel page allocator limits the size of maximal physically contiguous allocations. The limit is called MAX_PAGE_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.

The page size is not necessarily 4KB. For example, on 64-bit systems, 64KB pages can be enabled via PPC_64K_PAGES. Keep this in mind when choosing a value for this option.

Don't change if unsure.

Order of maximal physically contiguous allocations found in arch/nios2/Kconfig

The configuration item CONFIG_ARCH_FORCE_MAX_ORDER:

Help text

The kernel page allocator limits the size of maximal physically contiguous allocations. The limit is called MAX_PAGE_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.

Don't change if unsure.

Order of maximal physically contiguous allocations found in arch/m68k/Kconfig.cpu

The configuration item CONFIG_ARCH_FORCE_MAX_ORDER:

Help text

The kernel page allocator limits the size of maximal physically contiguous allocations. The limit is called MAX_PAGE_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.

For systems that have holes in their physical address space this value also defines the minimal size of the hole that allows freeing unused memory map.

Don't change if unsure.

Order of maximal physically contiguous allocations found in arch/arm/Kconfig

The configuration item CONFIG_ARCH_FORCE_MAX_ORDER:

Help text

The kernel page allocator limits the size of maximal physically contiguous allocations. The limit is called MAX_PAGE_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.

Don't change if unsure.

Maximum zone order found in arch/mips/Kconfig

The configuration item CONFIG_ARCH_FORCE_MAX_ORDER:

Help text

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 page size is not necessarily 4KB. Keep this in mind when choosing a value for this option.

Maximum zone order found in arch/loongarch/Kconfig

The configuration item CONFIG_ARCH_FORCE_MAX_ORDER:

Help text

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 page size is not necessarily 4KB. Keep this in mind when choosing a value for this option.

Maximum zone order found in arch/arc/Kconfig

The configuration item CONFIG_ARCH_FORCE_MAX_ORDER:

Help text

(none)

found in arch/arm64/Kconfig

The configuration item CONFIG_ARCH_FORCE_MAX_ORDER:

Help text

The kernel page allocator limits the size of maximal physically contiguous allocations. The limit is called MAX_PAGE_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.

The maximal size of allocation cannot exceed the size of the section, so the value of MAX_PAGE_ORDER should satisfy

MAX_PAGE_ORDER + PAGE_SHIFT <= SECTION_SIZE_BITS

Don't change if unsure.

found in arch/ia64/Kconfig

The configuration item CONFIG_ARCH_FORCE_MAX_ORDER:

Help text

(none)

Order of maximal physically contiguous allocations found in arch/arm64/Kconfig

The configuration item CONFIG_ARCH_FORCE_MAX_ORDER:

Help text

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.

The maximal size of allocation cannot exceed the size of the section, so the value of MAX_ORDER should satisfy

MAX_ORDER + PAGE_SHIFT <= SECTION_SIZE_BITS

Don't change if unsure.

MAX_ORDER (11 - 17) found in arch/ia64/Kconfig

The configuration item CONFIG_ARCH_FORCE_MAX_ORDER:

Help text

(none)

Maximum zone order found in arch/xtensa/Kconfig

The configuration item CONFIG_ARCH_FORCE_MAX_ORDER:

Help text

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.

This config option is actually maximum order plus one. For example, a value of 11 means that the largest free memory block is 2^10 pages.

Maximum zone order found in arch/sparc/Kconfig

The configuration item CONFIG_ARCH_FORCE_MAX_ORDER:

Help text

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.

This config option is actually maximum order plus one. For example, a value of 13 means that the largest free memory block is 2^12 pages.

Maximum zone order found in arch/sh/mm/Kconfig

The configuration item CONFIG_ARCH_FORCE_MAX_ORDER:

Help text

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.

This config option is actually maximum order plus one. For example, a value of 11 means that the largest free memory block is 2^10 pages.

The page size is not necessarily 4KB. Keep this in mind when choosing a value for this option.

Maximum zone order found in arch/powerpc/Kconfig

The configuration item CONFIG_ARCH_FORCE_MAX_ORDER:

Help text

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.

This config option is actually maximum order plus one. For example, a value of 11 means that the largest free memory block is 2^10 pages.

The page size is not necessarily 4KB. For example, on 64-bit systems, 64KB pages can be enabled via PPC_64K_PAGES. Keep this in mind when choosing a value for this option.

Maximum zone order found in arch/nios2/Kconfig

The configuration item CONFIG_ARCH_FORCE_MAX_ORDER:

Help text

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.

This config option is actually maximum order plus one. For example, a value of 11 means that the largest free memory block is 2^10 pages.

Maximum zone order found in arch/m68k/Kconfig.cpu

The configuration item CONFIG_ARCH_FORCE_MAX_ORDER:

Help text

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.

For systems that have holes in their physical address space this value also defines the minimal size of the hole that allows freeing unused memory map.

This config option is actually maximum order plus one. For example, a value of 11 means that the largest free memory block is 2^10 pages.

Maximum zone order found in arch/csky/Kconfig

The configuration item CONFIG_ARCH_FORCE_MAX_ORDER:

Help text

(none)

Maximum zone order found in arch/arm64/Kconfig

The configuration item CONFIG_ARCH_FORCE_MAX_ORDER:

Help text

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.

This config option is actually maximum order plus one. For example, a value of 11 means that the largest free memory block is 2^10 pages.

We make sure that we can allocate up to a HugePage size for each configuration. Hence we have : MAX_ORDER = (PMD_SHIFT - PAGE_SHIFT) + 1 => PAGE_SHIFT - 2

However for 4K, we choose a higher default value, 11 as opposed to 10, giving us 4M allocations matching the default size used by generic code.

Maximum zone order found in arch/arm/Kconfig

The configuration item CONFIG_ARCH_FORCE_MAX_ORDER:

Help text

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.

This config option is actually maximum order plus one. For example, a value of 11 means that the largest free memory block is 2^10 pages.

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