How is the size of init ram disk determined when initramfs is used?

[Nicholas Mc Guire]

On Sun, Jan 01, 2023 at 06:32:55PM +0100, Bernd Petrovitsch wrote:
> Hi all!
> 
> On 07/10/2022 04:32, Chan Kim wrote:
> [...]
> >I'm using initramfs.cpio.gz for initial file system image.
> >I embed it in the kernel Image file.
> >After linux boots, when I'm in the shell, I can create files.
> >But I'm curious how much the file system can grow.
> 
> Why not just try it once;-)

ramdisks are static - so if you mount ram0 and ramdisk_size=8192
then your ramdisk is occupying 8MB and that will be the hard limit
at least on some architectures (x86, I think also arm).

> 
> >I remember somewhere reading that the initramdisk is made and the initramfs
> >archive is extracted in the ramdisk.

On some architectures you can pass the size as kernel parameter
ramdisk_size=#kb and that will then set the size of the ramdisk
when you mount it (at boot or during normaal operations). 

As I did not find what archtiecture you are refering to this might
help - grep for ramdisk_size in Documentations and you should have
it. E.g. for arm it is marked as obsolete (arm/boot.rst) but still
seems to be supported with CONFIG_DEPRECATED_PARAM_STRUCT set. 
Wonder what it is being replaced by.

thx!
hofrat