tmux using 1G RAM even after clearing all scrollback history

Question

I use tmux (in fact byobu with tmux backend) on ubuntu 14.04.

My tmux uses 1GB of memory (VIRT and RES in top) and I have already used the clear-history command.

Now my scrollback is gone but the memory usage is not going down.

This tmux was running for a long time and lots of text scrolled through it. top shows it used more than 1 hour of CPU time in total.

What could be the reason?

Could there be a memory leak?

What could I try?

I cannot restart it or do dangerous things because the session runs an experiment that takes around one week more to complete...

Is your Bash/shell history somehow overriding the history of tmux? — , Aug 16 '14 at 01:28
How are you displaying cpu usage? Are you using tmux-mem-cpu-load? — Moonhead, Sep 10 '14 at 20:53
With tmux 1.9_a, memory usage of tmux reduces from 150M to 800k after typing ```reset``` in the shell. It may be a workaround. — Chih-Hsuan Yen, Nov 28 '14 at 20:40
When the issue occurs again I will try with tmux-mem-cpu-load. So far it did not happen though. — peschü, Dec 01 '14 at 08:18

score 10 · Answer 1 · answered Jan 21 '16 at 03:25

10

There seems to have been a bug in tmux, resulting in memory not being freed on a history clear.

This bug existed up to including version 1.9a, fixed in version 2.0. I'm posting this as a late answer, as version 1.9a seems to be still in use (with me at least).

https://groups.google.com/forum/#!topic/tmux-users/WiSZy6ft1As https://github.com/tmux/tmux/commit/28f23f18e9d79405a60348c4f7aeded33da9135b

answered Jan 21 '16 at 03:25

sstn

3,050
19
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My tmux 2.1 is still memory hungry :-( – Ciro Santilli OurBigBook.com Sep 28 '16 at 20:36
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Ah, forget it, it was because of `set -g @resurrect-capture-pane-contents 'on'`, that option is unusable. – Ciro Santilli OurBigBook.com Sep 29 '16 at 07:37

score 6 · Answer 2 · answered Sep 11 '14 at 03:30

Since no one has answered this, I'll offer my speculation on what's happening.

tmux allocates space in memory for its history, and that memory grows as you use up more of your history. Clearing history makes it invisible, but doesn't free up the actual memory. This means that tmux can use memory up the total number of lines for each open pane, regardless of whether those panes currently contain anything in them.

This is arguably a bug, or a bad feature at best.

I don't have a solution.

restarting `tmux` seems like the only option – alper Aug 08 '22 at 17:01 — alper, Aug 08 '22 at 17:01

score 4 · Answer 3 · answered Oct 31 '18 at 15:18

Necropost, but this problem has persisted for me until very recently. The memory use of tmux 2.6 from the repos on x86 xubuntu 18.04 always crept up to a gigabyte within a day or two. I removed it and built tmux 2.8 from source. Its memory usage has been minimal for several days. Problem solved, finally.

score 3 · Answer 4 · answered May 07 '18 at 12:37

Another memory leak was fixed in tmux 2.5:

* Handle slow terminals and fast output better: when the amount of data
  outstanding gets too large, discard output until it is drained and we are
  able to do a full redraw. Prevents tmux sitting on a huge buffer that the
  terminal will take forever to consume.

* Do not redraw a client unless we realistically think it can accept the data -
  defer redraws until the client has nothing else waiting to write.

https://github.com/tmux/tmux/blob/91b220525b0406763dafb6698d2741bec580bc10/CHANGES#L257-L263

score 2 · Answer 5 · answered Jan 13 '15 at 23:57

2

It's not a bug, tmux does free memory immediately when you clear the history. It's up to glibc to return it to the kernel and it is poor at that. You should be able to see the memory is free because if you clear the history at say 10000 lines, the memory usage will not grow again until the history again reaches 10000 lines.

answered Jan 13 '15 at 23:57

user4451397

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Would glibc return the memory to the kernel sooner if the machine is heavily swapping pages in and out (because it does not have any free memory left)? – peschü Jan 15 '15 at 05:59

tmux using 1G RAM even after clearing all scrollback history

5 Answers5