Re: lot of MemAvailable but falling cache and raising PSI

[Vlastimil Babka <vbabka@suse.cz>]

On 9/9/19 2:09 PM, Stefan Priebe - Profihost AG wrote:
> 
> Am 09.09.19 um 13:49 schrieb Vlastimil Babka:
>> On 9/9/19 10:54 AM, Stefan Priebe - Profihost AG wrote:
>>>> Do you have more snapshots of /proc/vmstat as suggested by Vlastimil and
>>>> me earlier in this thread? Seeing the overall progress would tell us
>>>> much more than before and after. Or have I missed this data?
>>>
>>> I needed to wait until today to grab again such a situation but from
>>> what i know it is very clear that MemFree is low and than the kernel
>>> starts to drop the chaches.
>>>
>>> Attached you'll find two log files.
>>
>> Thanks, what about my other requests/suggestions from earlier?
> 
> Sorry i missed your email.
> 
>> 1. How does /proc/pagetypeinfo look like?
> 
> # cat /proc/pagetypeinfo
> Page block order: 9
> Pages per block:  512

Looks like it might be fragmented, but was that snapshot taken in the 
situation where there's free memory and the system still drops cache?

>> 2. Could you also try if the bad trend stops after you execute:
>>   echo never > /sys/kernel/mm/transparent_hugepage/defrag
>> and report the result?
> 
> it's pretty difficult to catch those moments. Is it OK so set the value
> now and monitor if it happens again?

Well if it doesn't happen again after changing that setting, it would 
definitely point at THP interactions.

> Just to let you know:
> I've now also some more servers where memfree show 10-20Gb but cache
> drops suddently and memory PSI raises.

You mean those are in that state right now? So how does 
/proc/pagetypeinfo look there, and would changing the defrag setting help?

> Greets,
> Stefan
>