Re: [yocto] Memory requirements for building images with different architectures

[Mikko Rapeli <mikko.rapeli@linaro.org>]

Hi,

One related improvement is to avoid IO to disk completely as long as RAM is
available. By default file systems like ext4 will start writing all buffers
in the background after few seconds which is wasted IO if memory is available and
rm_work will anyway wipe the tmp to produce a target filesystem image tar ball etc.
sysctl settings are:

vm.dirty_background_bytes = 0
vm.dirty_background_ratio = 90
vm.dirty_expire_centisecs = 4320000
vm.dirtytime_expire_seconds = 432000
vm.dirty_bytes = 0
vm.dirty_ratio = 60
vm.dirty_writeback_centisecs = 0

http://events17.linuxfoundation.org/sites/events/files/slides/elce-2016-mario-goulart-mikko-rapeli.pdf

It the best case in-memory file systems like tmpfs will do but it's hard to estimate
the disk usage and memory size beforehand. Overflowing to disk IO only if RAM is
getting full scales better.

It makes sense to monitor build system CPU, memory, disk and network usage while builds are on
going. A lot of odd things will pop up, like IO bottlenecks (most CPUs idle), suprising network
downloads.

And deleting files is a heavy operation and if flushed to disk, it's annoyingly slow
compared to wiping an entire partition and creating a new file system on it.

Cheers,

-Mikko