Comment 75 for bug 1833281

(In reply to ValdikSS from comment #53)
> Recently, about since kernel 5.2.7, the issue is either gone or present to
> much less extent.
> Right now I'm running kernel 5.2.11 and finally I can keel Firefox and
> VirtualBox running at the same time, with 3G+ in swap, and the system does
> not freeze.
>
> Could anyone affected by this issue try newer kernels?

First of all, did you reset all your custom sysctls to default values?

1) One user (ilfat@) reported that:
1.1) on kernels 4.19.57 and Ubuntu kernel 4.15.0-54 his system did not swap correctly: all memory was full but only a small part of the swap was used, that lead to freezes
1.2) on kernels 4.19.67 and Ubuntu kernels 4.15.0-60, 4.15.0-62 systemd swaps in general normally, but he tweaked vm.watermark_scale_factor to make it swap better
1.3) Ilfat had exactly the same problem on both ext4 and btrfs

So, something was fixed in upstream, backported to LTS kernel 4.19 and to Ubuntu kernel. I don't know what. And that issue is 100% not in BTRFS but is another problem or another aspect of the problem.

2) I did not see much difference between Ubuntu kernels 54 and 60, 62 in what is described in comment#51. So, that mystereous fix did not help.

3) another user (anreas@) reports the same as in (2):
https://forum.rosalinux.ru/viewtopic.php?p=101903&sid=621857320f4d1a566e0cfa6e80ff4a8c#p101903

4) trying to overcome issues from comment#51, I built Ubuntu kernel 4.15.0 with 2 pathes:

* https://abf.io/mikhailnov/kernel-desktop-4.15/blob/master/le9-rosa.patch
* https://abf.io/mikhailnov/kernel-desktop-4.15/blob/master/Chromium-OS-low-memory-patchset.patch

and set kernel options:
# https://bugzilla.kernel.org/show_bug.cgi?id=196729#c36
vm.watermark_scale_factor=100
vm.unevictable_activefile_kbytes=100000
#vm.swappiness=80
# https://bugs.chromium.org/p/chromium/issues/detail?id=263561#c16
# Disable swap read-ahead
vm.page-cluster=0

After that, I _thank_ it became a bit better (I cannot prove it by numbers, just was unbale to make the system become inresponsive, but LA remained the same), but unfortunately the main user of that notebook did not use it for some days and so right now I can't say that according to her feedback the situation has improved and the system does not microfreeze from time to time anymore. Let's wait a bit more. And still that may be a coincidence, not the result of patches and/or tweaked sysctls.

I was able to dead lock that system by openning too many tabs in Chromium, but that is not what those patches should have solved. nohang/earlymoon would have probably helped if it was used.

>
> Mikhail, I have a spare laptop which I can setup for you for tests. Do you
> have time and wish to investigate this issue?

I don't have ideas how to investigate it. And how to measure the result. Maybe PSI can tell something, I did not try to look at them. And even more, I don't understand what the problem is ;)