sunxi64: Decrease amount of (video?) reserved memory

[vmspike]

Is it a way to reduce the amount of reserved memory on sunxi64 devices?

 

Trying to remove all useless for my case features (video/audio/wireless) to free up memory/resources for other tasks.

 

The amount of total (413M) vs real (512M) memory is quite low:

# grep -e Mem -e Cma /proc/meminfo
MemTotal:         422416 kB
MemFree:           49620 kB
MemAvailable:     314396 kB
CmaTotal:              0 kB
CmaFree:               0 kB

# dmesg | grep Memory:
[    0.000000] Memory: 407924K/524288K available (14144K kernel code, 1456K rwdata, 8700K rodata, 3072K init, 521K bss, 116364K reserved, 0K cma-reserved)

# grep extraargs /boot/armbianEnv.txt
extraargs=cma=0 sunxi_no_mali_mem_reserve sunxi_ve_mem_reserve=0 sunxi_g2d_mem_reserve=0 sunxi_fb_mem_reserve=16

# uname -a
Linux pi160 6.6.65-current-sunxi64 #1 SMP Wed Dec 11 19:13:43 +04 2024 aarch64 GNU/Linux

 

The tricks which works for `sunxi` (e.g. `orangepizero`) does not work for `sunxi64`  boards:

https://linux-sunxi.org/Kernel_arguments

 

Attempt to specify that extraargs in /boot/armbianEnv.txt have no effect (also their defaults are absent in /boot/boot.cmd, while present in orangepizero's version), except for `cma=0` with is not directly related to total available memory.

Custom kernel with `CONFIG_CMA=n` also changes nothing.

Edited January 4 by vmspike

[vmspike]

The same case was already discussed here, but with no result:

 

Finally found that adding `swiotlb=1` to kernel args releases 64 MB of memory:

/boot/armbianEnv.txt:extraargs=... nokaslr cma=0 swiotlb=0

but not disables it completely:

[    0.000000] software IO TLB: SWIOTLB bounce buffer size roundup to 1MB

Now:

MemTotal: 487684 kB

 

Alternative option `iommu=off` does not work.
 

So it's not for graphics.

This option looks reasonable for less than 4 GB RAM devices(?)

If someone knows potential drawbacks, please disclose.

 

Edited March 5 by vmspike