Re: lot of MemAvailable but falling cache and raising PSI

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On Tue 10-09-19 15:14:45, Stefan Priebe - Profihost AG wrote:
> Am 10.09.19 um 15:05 schrieb Stefan Priebe - Profihost AG:
> > 
> > Am 10.09.19 um 14:57 schrieb Michal Hocko:
> >> On Tue 10-09-19 14:45:37, Stefan Priebe - Profihost AG wrote:
> >>> Hello Michal,
> >>>
> >>> ok this might take a long time. Attached you'll find a graph from a
> >>> fresh boot what happens over time (here 17 August to 30 August). Memory
> >>> Usage decreases as well as cache but slowly and only over time and days.
> >>>
> >>> So it might take 2-3 weeks running Kernel 5.3 to see what happens.
> >>
> >> No problem. Just make sure to collect the requested data from the time
> >> you see the actual problem. Btw. you try my very dumb scriplets to get
> >> an idea of how much memory gets reclaimed due to THP.
> > 
> > You mean your sed and sort on top of the trace file? No i did not with
> > the current 5.3 kernel do you think it will show anything interesting?
> > Which line shows me how much memory gets reclaimed due to THP?

Please re-read http://lkml.kernel.org/r/20190910082919.GL2063@xxxxxxxxxxxxxx
Each command has a commented output. If you see nunmber of reclaimed
pages to be large for GFP_TRANSHUGE then you are seeing a similar
problem.

> Is something like a kernel memory leak possible? Or wouldn't this end up
> in having a lot of free memory which doesn't seem usable.

I would be really surprised if this was the case.

> I also wonder why a reclaim takes place when there is enough memory.

This is not clear yet and it might be a bug that has been fixed since
4.18. That's why we need to see whether the same is pattern is happening
with 5.3 as well.

-- 
Michal Hocko
SUSE Labs




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