I've been going through all boot scripts, just to get to know OpenWrt better. The current script I'm working on is init.d/sysctl and I have some questions if someone is willing to answer them.
Now this script seems untouched in forever reading the copyright statement. A lot has changed since then, memory included, does it still hold up today?
vm.min_free_kbytes is set to prevent system instability under heavy memory utilization which is more of a problem for memory constraint devices I think because that limit can be reached more easily.
Converting the OpenWrt table of hardware into sql and dumping out rammb's unique values this gave me a 2^x list:
16,32,64,128,256,512,1024,2048,4096,8192
Reading up on different locations because docs.kernel.org for me is a bit lacking in its description regarding recommendations and use cases, I found that widely used settings ranges between 1%~5% when it comes to servers.
The current code has 3 options:
- greater than 65536 kb which is 128M+ reserves 16M
- greater than 32768 kb which is 64M reserves 8M
- and less than 64M reserves 1M
My assumption when reading the code that it compensates for the fact that the amount of memory in /proc/meminfo is always a bit less, forcing it to take one stepback. This way 127M will still reserve 16M.
At this point I have the following questions:
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Did I read the code correctly ?
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What is the reason behind reserving 12.5% for 64M-128M devices?
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Would reserving more memory for high memory devices have any benefits or
is 16M enough?
Personally I found that 1 out of every 32mb set aside gives an acceptable number
for high-memory device if more is needed, but deviates quite a bit:
total memory : 16,32,64,128,256,512,1024,2048,4096,8192
reserved in code: 1, 1, 8, 16, 16, 16, 16, 16, 16, 16
1/32M (~3%) : 1, 1, 2, 4, 8, 16, 32, 64, 128, 256
Thanks in advance.
but no, I was focused on the more memory rich devices.