Web lists-archives.com

Re: Swap priority in Debian






On Saturday 25 August 2018 04:29 PM, Reco wrote:
	Hi.

On Sat, Aug 25, 2018 at 09:42:31AM +0530, Subhadip Ghosh wrote:
Hi,

I am a Debian testing user. Recently I am experiencing freezing on my Debian
system intermittently and during troubleshooting the same, I found out that
the I have a swap partition with priority set to -2.
Same here with stable.


But according to the below manpage:

https://manpages.debian.org/stretch/mount/swapon.8.en.html

swap priority should be between -1 and 32767.
So swapon(8) utility has this restriction. Note that the system call
itself - swapon(2) merely interprets swap priority as a signed integer,
so any priority number is actually possible (within integer limits of
course).


I have a swappiness value of 60 but I don't remember seeing the swap
being used at all recently, the used swap is always 0%.
A hint. They invented this wonderful thing called sysstat decades ago so
you don't have to remember your swap usage, along with other things
sysstat gathers.


My question is, do you think that the -2 priority is stopping the swap
partition from actually being used and because of that, the system is
getting frozen when the memory usage is high?
No, it definitely does not work this way.
A swap priority only comes into play once you have multiple instances of
swaps. If you have a single swap partition/lv/file, a priority value is
meaningless.

A system freezes, on the other hand (did I mention sysstat?), could
indicate heavy swapping, barrier writes, kernel bugs (12309, anyone?),
oom killer invocations, overheating and many other things.
A good starting point would be kernel message log (aka
/var/log/kern.log) from the time of this freeze.
Thanks for the suggestion. I checked the kern.log but did not find any suspicious log, in fact no entry from that exact time frame when the last freeze happened. Do you have any other suggestions to troubleshoot the freezes?