CONFIG_HIGHMEM: High Memory Support

General informations

The Linux kernel configuration item CONFIG_HIGHMEM has multiple definitions:

High Memory Support found in arch/xtensa/Kconfig

The configuration item CONFIG_HIGHMEM:

• prompt: High Memory Support
• type: bool
• depends on: CONFIG_MMU
• defined in arch/xtensa/Kconfig
• found in Linux kernels: 3.15–3.19, 4.0–4.20, 5.0–5.19, 6.0–6.12, 6.13-rc+HEAD

Help text

Linux can use the full amount of RAM in the system by default. However, the default MMUv2 setup only maps the lowermost 128 MB of memory linearly to the areas starting at 0xd0000000 (cached) and 0xd8000000 (uncached). When there are more than 128 MB memory in the system not all of it can be "permanently mapped" by the kernel. The physical memory that's not permanently mapped is called "high memory".

If you are compiling a kernel which will never run on a machine with more than 128 MB total physical RAM, answer N here.

If unsure, say Y.

High memory support found in arch/powerpc/Kconfig

The configuration item CONFIG_HIGHMEM:

• prompt: High memory support
• type: bool
• depends on: CONFIG_PPC32
• defined in arch/powerpc/Kconfig
• found in Linux kernels: 2.6.15–2.6.39, 3.0–3.19, 4.0–4.20, 5.0–5.19, 6.0–6.12, 6.13-rc+HEAD

Help text

(none)

High Memory Support found in arch/mips/Kconfig

The configuration item CONFIG_HIGHMEM:

• prompt: High Memory Support
• type: bool
• depends on: CONFIG_32BIT && CONFIG_CPU_SUPPORTS_HIGHMEM && CONFIG_SYS_SUPPORTS_HIGHMEM && ! CONFIG_CPU_MIPS32_3_5_EVA
• defined in arch/mips/Kconfig
• found in Linux kernels: 2.6.0–2.6.39, 3.0–3.19, 4.0–4.20, 5.0–5.19, 6.0–6.12, 6.13-rc+HEAD

Help text

(none)

High memory support found in arch/microblaze/Kconfig

The configuration item CONFIG_HIGHMEM:

• prompt: High memory support
• type: bool
• depends on: (none)
• defined in arch/microblaze/Kconfig
• found in Linux kernels: 3.4–3.19, 4.0–4.20, 5.0–5.19, 6.0–6.12, 6.13-rc+HEAD

Help text

The address space of Microblaze processors is only 4 Gigabytes large and it has to accommodate user address space, kernel address space as well as some memory mapped IO. That means that, if you have a large amount of physical memory and/or IO, not all of the memory can be "permanently mapped" by the kernel. The physical memory that is not permanently mapped is called "high memory".

If unsure, say n.

High Memory Support found in arch/csky/Kconfig

The configuration item CONFIG_HIGHMEM:

• prompt: High Memory Support
• type: bool
• depends on: ! CONFIG_CPU_CK610
• defined in arch/csky/Kconfig
• found in Linux kernels: 4.20, 5.0–5.19, 6.0–6.12, 6.13-rc+HEAD

Help text

(none)

High Memory Support found in arch/arm/Kconfig

The configuration item CONFIG_HIGHMEM:

• prompt: High Memory Support
• type: bool
• depends on: CONFIG_MMU
• defined in arch/arm/Kconfig
• found in Linux kernels: 3.0–3.19, 4.0–4.20, 5.0–5.19, 6.0–6.12, 6.13-rc+HEAD

Help text

The address space of ARM processors is only 4 Gigabytes large and it has to accommodate user address space, kernel address space as well as some memory mapped IO. That means that, if you have a large amount of physical memory and/or IO, not all of the memory can be "permanently mapped" by the kernel. The physical memory that is not permanently mapped is called "high memory".

Depending on the selected kernel/user memory split, minimum vmalloc space and actual amount of RAM, you may not need this option which should result in a slightly faster kernel.

If unsure, say n.

High Memory Support found in arch/arc/Kconfig

The configuration item CONFIG_HIGHMEM:

• prompt: High Memory Support
• type: bool
• depends on: (none)
• defined in arch/arc/Kconfig
• found in Linux kernels: 4.4–4.20, 5.0–5.19, 6.0–6.12, 6.13-rc+HEAD

Help text

With ARC 2G:2G address split, only upper 2G is directly addressable by kernel. Enable this to potentially allow access to rest of 2G and PAE in future

found in arch/x86/Kconfig

The configuration item CONFIG_HIGHMEM:

• prompt:
• type: bool
• depends on: CONFIG_X86_32 && ( CONFIG_HIGHMEM64G || CONFIG_HIGHMEM4G )
• defined in arch/x86/Kconfig
• found in Linux kernels: 2.6.24–2.6.39, 3.0–3.19, 4.0–4.20, 5.0–5.19, 6.0–6.12, 6.13-rc+HEAD

Help text

(none)

found in arch/sparc/Kconfig

The configuration item CONFIG_HIGHMEM:

• prompt:
• type: bool
• depends on: CONFIG_SPARC32
• defined in arch/sparc/Kconfig
• found in Linux kernels: 2.5.45–2.5.75, 2.6.0–2.6.39, 3.0–3.19, 4.0–4.20, 5.0–5.19, 6.0–6.12, 6.13-rc+HEAD

Help text

(none)

High Memory Support found in arch/nds32/Kconfig.cpu

The configuration item CONFIG_HIGHMEM:

• prompt: High Memory Support
• type: bool
• depends on: CONFIG_MMU && ! CONFIG_CPU_CACHE_ALIASING
• defined in arch/nds32/Kconfig.cpu
• found in Linux kernels: 4.17–4.20, 5.0–5.17, 5.17+HEAD

Help text

The address space of Andes processors is only 4 Gigabytes large and it has to accommodate user address space, kernel address space as well as some memory mapped IO. That means that, if you have a large amount of physical memory and/or IO, not all of the memory can be "permanently mapped" by the kernel. The physical memory that is not permanently mapped is called "high memory".

Depending on the selected kernel/user memory split, minimum vmalloc space and actual amount of RAM, you may not need this option which should result in a slightly faster kernel.

If unsure, say N.

High Memory Support found in arch/metag/Kconfig

The configuration item CONFIG_HIGHMEM:

• prompt: High Memory Support
• type: bool
• depends on: (none)
• defined in arch/metag/Kconfig
• found in Linux kernels: 3.9–3.19, 4.0–4.16

Help text

The address space of Meta processors is only 4 Gigabytes large and it has to accommodate user address space, kernel address space as well as some memory mapped IO. That means that, if you have a large amount of physical memory and/or IO, not all of the memory can be "permanently mapped" by the kernel. The physical memory that is not permanently mapped is called "high memory".

Depending on the selected kernel/user memory split, minimum vmalloc space and actual amount of RAM, you may not need this option which should result in a slightly faster kernel.

If unsure, say n.

High memory support found in arch/frv/Kconfig

The configuration item CONFIG_HIGHMEM:

• prompt: High memory support
• type: bool
• depends on: CONFIG_MMU
• defined in arch/frv/Kconfig
• found in Linux kernels: 2.6.11–2.6.39, 3.0–3.19, 4.0–4.16

Help text

If you wish to use more than 256MB of memory with your MMU based system, you will need to select this option. The kernel can only see the memory between 0xC0000000 and 0xD0000000 directly... everything else must be kmapped.

The arch is, however, capable of supporting up to 3GB of SDRAM.

found in arch/tile/Kconfig

The configuration item CONFIG_HIGHMEM:

• prompt:
• type: bool
• depends on: (none)
• defined in arch/tile/Kconfig
• found in Linux kernels: 2.6.36–2.6.39, 3.0–3.19, 4.0–4.16

Help text

Linux can use the full amount of RAM in the system by default. However, the address space of TILE processors is only 4 Gigabytes large. That means that, if you have a large amount of physical memory, not all of it can be "permanently mapped" by the kernel. The physical memory that's not permanently mapped is called "high memory".

If you are compiling a kernel which will never run on a machine with more than 512 MB total physical RAM, answer "false" here. This will result in the kernel mapping all of physical memory into the top 1 GB of virtual memory space.

If unsure, say "true".

found in arch/mn10300/Kconfig

The configuration item CONFIG_HIGHMEM:

• prompt:
• type: bool
• depends on: (none)
• defined in arch/mn10300/Kconfig
• found in Linux kernels: 2.6.25–2.6.39, 3.0–3.19, 4.0–4.16

Help text

(none)

Highmem support found in arch/um/Kconfig.um

The configuration item CONFIG_HIGHMEM:

• prompt: Highmem support
• type: bool
• depends on: ! CONFIG_64BIT && CONFIG_BROKEN
• defined in arch/um/Kconfig.um
• found in Linux kernels: 3.9–3.19, 4.0

Help text

This was used to allow UML to run with big amounts of memory. Currently it is unstable, so if unsure say N.

To use big amounts of memory, it is recommended enable static linking (i.e. STATIC_LINK) - this should allow the guest to use up to 2.75G of memory.

Highmem support (EXPERIMENTAL) found in arch/um/Kconfig.um

The configuration item CONFIG_HIGHMEM:

• prompt: Highmem support (EXPERIMENTAL)
• type: bool
• depends on: ! CONFIG_64BIT && CONFIG_BROKEN
• defined in arch/um/Kconfig.um
• found in Linux kernels: 2.6.28–2.6.39, 3.0–3.8

Help text

This was used to allow UML to run with big amounts of memory. Currently it is unstable, so if unsure say N.

To use big amounts of memory, it is recommended enable static linking (i.e. STATIC_LINK) - this should allow the guest to use up to 2.75G of memory.

found in arch/c6x/Kconfig

The configuration item CONFIG_HIGHMEM:

• prompt:
• type: bool
• depends on: (none)
• defined in arch/c6x/Kconfig
• found in Linux kernels: 3.3–3.4

Help text

(none)

High Memory Support (EXPERIMENTAL) found in arch/arm/Kconfig

The configuration item CONFIG_HIGHMEM:

• prompt: High Memory Support (EXPERIMENTAL)
• type: bool
• depends on: CONFIG_MMU && CONFIG_EXPERIMENTAL
• defined in arch/arm/Kconfig
• found in Linux kernels: 2.6.30–2.6.39

Help text

The address space of ARM processors is only 4 Gigabytes large and it has to accommodate user address space, kernel address space as well as some memory mapped IO. That means that, if you have a large amount of physical memory and/or IO, not all of the memory can be "permanently mapped" by the kernel. The physical memory that is not permanently mapped is called "high memory".

Depending on the selected kernel/user memory split, minimum vmalloc space and actual amount of RAM, you may not need this option which should result in a slightly faster kernel.

If unsure, say n.

High memory support found in arch/xtensa/Kconfig

The configuration item CONFIG_HIGHMEM:

• prompt: High memory support
• type: bool
• depends on: (none)
• defined in arch/xtensa/Kconfig
• found in Linux kernels: 2.6.13–2.6.28

Help text

(none)

Highmem support (EXPERIMENTAL) found in arch/um/Kconfig

The configuration item CONFIG_HIGHMEM:

• prompt: Highmem support (EXPERIMENTAL)
• type: bool
• depends on: ! CONFIG_64BIT && CONFIG_EXPERIMENTAL
• defined in arch/um/Kconfig
• found in Linux kernels: 2.6.16–2.6.27

Help text

This was used to allow UML to run with big amounts of memory. Currently it is unstable, so if unsure say N.

To use big amounts of memory, it is recommended enable static linking (i.e. STATIC_LINK) - this should allow the guest to use up to 2.75G of memory.

High memory support found in arch/ppc/Kconfig

The configuration item CONFIG_HIGHMEM:

• prompt: High memory support
• type: bool
• depends on: (none)
• defined in arch/ppc/Kconfig
• found in Linux kernels: 2.5.45–2.5.75, 2.6.0–2.6.26

Help text

(none)

found in arch/i386/Kconfig

The configuration item CONFIG_HIGHMEM:

• prompt:
• type: bool
• depends on: CONFIG_HIGHMEM64G || CONFIG_HIGHMEM4G
• defined in arch/i386/Kconfig
• found in Linux kernels: 2.5.45–2.5.75, 2.6.0–2.6.23

Help text

(none)

Highmem support found in arch/um/Kconfig

The configuration item CONFIG_HIGHMEM:

• prompt: Highmem support
• type: bool
• depends on: ! CONFIG_64BIT
• defined in arch/um/Kconfig
• found in Linux kernels: 2.5.45–2.5.75, 2.6.0–2.6.15

Help text

(none)

High Memory Support found in arch/mips/Kconfig-shared

The configuration item CONFIG_HIGHMEM:

• prompt: High Memory Support
• type: bool
• depends on: CONFIG_MIPS32 && ( CONFIG_CPU_R3000 || CONFIG_CPU_SB1 || CONFIG_CPU_R7000 || CONFIG_CPU_R10000 ) && !( CONFIG_BAGET_MIPS || CONFIG_DECSTATION )
• defined in arch/mips/Kconfig-shared
• found in Linux kernels: 2.5.74–2.5.75

Help text

(none)

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