Specifies how much memory, in megabytes, to reserve for the exclusive use of the GPU: the remaining memory is allocated to the ARM CPU for use by the OS. For Pis with less than 1GB of memory, the default is 64; for Pis with 1GB or more of memory the default is 76.
The memory allocated to the GPU is used for display, 3D, Codec and camera purposes as well as some basic firmware housekeeping. The maximums specified below assume you are using all these features. If you are not, then smaller values of gpu_mem can be used.
To ensure the best performance of Linux, you should set gpu_mem to the lowest possible value. If a particular graphics feature is not working correctly, try increasing the value of gpu_mem, being mindful of the recommended maximums shown below. Unlike GPU's found on x86 machines, where increasing memory can improve 3D performance, the architecture of the VideoCore means there is no performance advantage from specifying values larger than is necessary, and in fact it can harm performance.
On the Raspberry Pi 4 the 3D component of the GPU has its own memory management unit (MMU), and does not use memory from the gpu_mem allocation. Instead memory is allocated dynamically within Linux. This allows a smaller value to be specified for gpu_mem on the Pi 4, compared to previous models.
The recommended maximum values are as follows:
| total RAM | gpu_mem recommended maximum |
|---|---|
| 256MB | 128 |
| 512MB | 384 |
| 1GB or greater | 512, 256 on the Pi4 |
It is possible to set gpu_mem to larger values, however this should be avoided since it can cause problems, such as preventing Linux from booting. The minimum value is 16, however this disables certain GPU features.
You can also use gpu_mem_256, gpu_mem_512, and gpu_mem_1024 to allow swapping the same SD card between Pis with different amounts of RAM without having to edit config.txt each time:
The gpu_mem_256 command sets the GPU memory in megabytes for Raspberry Pis with 256MB of memory. (It is ignored if memory size is not 256MB). This overrides gpu_mem.
The gpu_mem_512 command sets the GPU memory in megabytes for Raspberry Pis with 512MB of memory. (It is ignored if memory size is not 512MB). This overrides gpu_mem.
The gpu_mem_1024 command sets the GPU memory in megabytes for Raspberry Pis with 1GB or more of memory. (It is ignored if memory size is smaller than 1GB). This overrides gpu_mem.
This parameter can be used to force a Raspberry Pi to limit its memory capacity: specify the total amount of RAM, im megabytes, you wish the Pi to use. For example, to make a 4GB Raspberry Pi 4B behave as though it were a 1GB model, use the following:
total_mem=1024
This value will be clamped between a minimum of 128MB, and a maximum of the total memory installed on the board.
Setting this to 1 disables the CPU's access to the GPU's L2 cache and requires a corresponding L2 disabled kernel. Default value on BCM2835 is 0. On BCM2836, BCM2837, and BCM2711, the ARMs have their own L2 cache and therefore the default is 1. The standard Pi kernel.img and kernel7.img builds reflect this difference in cache setting.
This article uses content from the eLinux wiki page RPiconfig, which is shared under the Creative Commons Attribution-ShareAlike 3.0 Unported license