Re: OOM-killer not being involked under memory pressure

[Pariksheet Nanda <pariksheet.nanda@protonmail.com>]

>> The hanging behavior is like a step function: the computer goes from being
>> fully responsive to completely unresponsive;
>
> That's very much unlike a normal "out of RAM" situation, OTOH.
> Normally what happens is that the OS starts to shuffle things around
> (throwing out cached data, moving other to swap, etc...) making the
> machine slower and slower.
>
> The step function sounds much more like a bug such as a deadlock.

Thank you for clearing up my misunderstanding of the observed behavior!  Indeed, Linux-Fan linked to the swap deadlock issue with ZFS.


> You could run a`memtester` process and tell it to test, say 6GB, so you
> the kernel only has 2GB left to play with and it will be forced to push
> stuff to swap, which you should then see in the output of `free`.

Thank you to you, Charles, and Tixy, for the suggestion to use `free`; I had only previously used it to check RAM usage and did not know it's usefulness to also check swap.  As Tixy mentions, `free` does show zeros now that I have swap disabled:

$ free
              total        used        free      shared  buff/cache   available
Mem:        8100708     4136324     2972808      197340      991576     3597312
Swap:             0           0           0


> You might want to try and set that same machine up with an ext4
> filesystem instead temporarily to see if you can reproduce the problem
> even without the use of ZFS (depending on how ZFS is used and your disk
> setup, it might be possible to do it easily, without having to
> reinstall (which could result in a sufficiently different system that
> it'd then be hard to convince oneself that the only difference is
> ZFS-vs-ext4)).

I actually was using ext4 for a few years on this machine before switching to ZFS in June and it behaved well, right up to the point where it didn't - I have had a few long power outages in my rural area, and running LUKS on LVM with ext4 after 1 particular power outage made it irrecoverable with my abilities.  Which is why I switched to using encrypted ZFS.  Though I in no way wish to suggest encrypted ZFS is more reliable than LUKS on LVM with ext4; minus the encryption, my colleagues have had fewer instances of disk corription with ZFS and so I'm experimenting with it.


> Stefan

Pariksheet