CONFIG_CMA_ALIGNMENT: Maximum PAGE_SIZE order of alignment for contiguous buffers

General informations

The Linux kernel configuration item CONFIG_CMA_ALIGNMENT has multiple definitions:

Maximum PAGE_SIZE order of alignment for contiguous buffers found in kernel/dma/Kconfig

The configuration item CONFIG_CMA_ALIGNMENT:

• prompt: Maximum PAGE_SIZE order of alignment for contiguous buffers
• type: int
• depends on: (none)
• defined in kernel/dma/Kconfig
• found in Linux kernels: 5.1–5.19, 6.0–6.12, 6.13-rc+HEAD

Help text

DMA mapping framework by default aligns all buffers to the smallest PAGE_SIZE order which is greater than or equal to the requested buffer size. This works well for buffers up to a few hundreds kilobytes, but for larger buffers it just a memory waste. With this parameter you can specify the maximum PAGE_SIZE order for contiguous buffers. Larger buffers will be aligned only to this specified order. The order is expressed as a power of two multiplied by the PAGE_SIZE.

For example, if your system defaults to 4KiB pages, the order value of 8 means that the buffers will be aligned up to 1MiB only.

If unsure, leave the default value "8".

Maximum PAGE_SIZE order of alignment for contiguous buffers found in drivers/base/Kconfig

The configuration item CONFIG_CMA_ALIGNMENT:

• prompt: Maximum PAGE_SIZE order of alignment for contiguous buffers
• type: int
• depends on: (none)
• defined in drivers/base/Kconfig
• found in Linux kernels: 3.5–3.19, 4.0–4.20, 5.0

Help text

DMA mapping framework by default aligns all buffers to the smallest PAGE_SIZE order which is greater than or equal to the requested buffer size. This works well for buffers up to a few hundreds kilobytes, but for larger buffers it just a memory waste. With this parameter you can specify the maximum PAGE_SIZE order for contiguous buffers. Larger buffers will be aligned only to this specified order. The order is expressed as a power of two multiplied by the PAGE_SIZE.

For example, if your system defaults to 4KiB pages, the order value of 8 means that the buffers will be aligned up to 1MiB only.

If unsure, leave the default value "8".

Hardware

LKDDb

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• (none)

Sources

This page is automaticly generated with free (libre, open) software lkddb(see lkddb-sources).

The data is retrived from:

• Linux kernel
• Linux Kernel Driver DataBase (LKDDb)

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