Re: Let's talk about the elephant in the room - the Linux kernel's inability to gracefully handle low memory pressure

[Vlastimil Babka]

On 8/4/19 11:23 AM, Artem S. Tashkinov wrote:
> Hello,
> 
> There's this bug which has been bugging many people for many years
> already and which is reproducible in less than a few minutes under the
> latest and greatest kernel, 5.2.6. All the kernel parameters are set to
> defaults.
> 
> Steps to reproduce:
> 
> 1) Boot with mem=4G
> 2) Disable swap to make everything faster (sudo swapoff -a)
> 3) Launch a web browser, e.g. Chrome/Chromium or/and Firefox
> 4) Start opening tabs in either of them and watch your free RAM decrease
> 
> Once you hit a situation when opening a new tab requires more RAM than
> is currently available, the system will stall hard. You will barely  be
> able to move the mouse pointer. Your disk LED will be flashing
> incessantly (I'm not entirely sure why). You will not be able to run new
> applications or close currently running ones.

> This little crisis may continue for minutes or even longer. I think
> that's not how the system should behave in this situation. I believe
> something must be done about that to avoid this stall.

Yeah that's a known problem, made worse SSD's in fact, as they are able
to keep refaulting the last remaining file pages fast enough, so there
is still apparent progress in reclaim and OOM doesn't kick in.

At this point, the likely solution will be probably based on pressure
stall monitoring (PSI). I don't know how far we are from a built-in
monitor with reasonable defaults for a desktop workload, so CCing
relevant folks.

> I'm almost sure some sysctl parameters could be changed to avoid this
> situation but something tells me this could be done for everyone and
> made default because some non tech-savvy users will just give up on
> Linux if they ever get in a situation like this and they won't be keen
> or even be able to Google for solutions.
> 
> 
> Best regards,
> Artem
>