Ubuntu 20.04 has recently started to use swap very aggressively

Markus

3/25/23, 6:36 AM

I use Ubuntu 20.04 with 16 GB RAM and a swappiness setting of 10. This has worked well in the past, but sometime during the last month I feel there has been a huge shift in the way memory is handled. Recently the machine has started using swap very aggressively if left unused for a while, even if there is plenty of space left in RAM. The result is that if I leave the machine overnight with a few programs running I will have to spend several minutes the next morning waiting for it to retrieve the running programs and desktop environment from swap where they are needlessly stowed even though there is plenty of free RAM. Where can this behaviour come from, and how could I modify it back to previous?

Edit: Along the lines that @rfm suggested I wrote a small script that checked memfree every 15 minutes, and also logged the output of px at the same time. Unfortunately this didn't reveal much. It was plain to see that the memory filled up after a few hours, but no running program used that much memory, instead it was the "cached" caption of meminfo that showed an increase, starting at a small part of memory but increased to the full amount of ram. Sadly I'm still no closer to knowing why this has started to happen.

0 + 0

swap

memory-usage

ram

20.04

Someone

3/25/23, 6:39 AM

What is the output of `uname -r`

rfm

3/25/23, 7:15 AM

I would suspect there's some transient process, like a cron job, that fires up overnight and demands a lot of memory, forcing other stuff to swap out. Might be hard to find it, perhaps a script that checks MemFree in /proc/meminfo periodically and looks for drops. it could even log a 'px -ax' to try to catch the culprit.

Tilman

3/25/23, 7:56 AM

@rfm - I suggest you post that as an answer.

Markus

3/26/23, 7:03 AM

@Algnis: 5.4.0-90-lowlatency

Markus

3/26/23, 7:05 AM

@rfm: Off the top of my head I don't know any cron jobs I'm running that would do this, but your suggestion for a script is a good one, thanks.

Elon Musk

I sit in a Tesla and translated this thread with Ai:

EN: Ubuntu 20.04 has recently started to use swap very aggressively

TH: Ubuntu 20.04 เพิ่งเริ่มใช้ swap อย่างจริงจัง

RO: Ubuntu 20.04 a început recent să folosească swap foarte agresiv

RU: Ubuntu 20.04 недавно начал очень агрессивно использовать своп.

VI: Ubuntu 20.04 gần đây đã bắt đầu sử dụng trao đổi rất tích cực

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