Create a swapfile for your Linux server

This was covered upstream, please scroll up. May cause problems later if the swapfile is fragmented.

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I came back to this zRam/zSwap idea and decided to give it a longer test run on my low traffic site hosted on a 1GB Digital Ocean slice. Actually the idea came back and Microsoft just enabled RAM compression for all users on Windows 10 and it seems to be doing its job on my cheap Baytrail tablet.

Anyway, been running for 24 hours now and so far the system has not yet touched the physical swap at all. I also radjusted the Swappiness back to default value 60, rather than 10.

FatMoomin:~# cat /proc/swaps
Filename                                Type            Size    Used    Priority
/swapfile                               file            2097148 0       -1
/dev/zram0                              partition       508936  208060  5

So far nothing unusual in the CPU loads either, but again this is a low traffic site. Few hundred views per day and most are passive readers.

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Hi !

I have a question : I created a 1 GB swapfile, it is activated and works for months now but it’s recommanded to use a 2 GB swap for my config, what will be the command to increase it to a 2 GB swapfile ?

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swapoff /swapfile and follow the directions to make a 2GB swapfile.

You don’t need to re-do the file system table, swappiness and so on.

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Thanks It worked

If it helps others, I’ll give a little extra : I had to stop the app because the server couldn’t allocate the memory. So I run these commands :

cd /var/discourse
./launcher stop app

I run the command @pfaffman gave me, did a new swap, started the app and rebooted my server

cd /var/discourse
./launcher start app

Then for the reboot : shutdown -r now (I don’t know if it was neccessary, but it never hurts)

And voilà

Thanks again !

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but if the swappiness is 10, isn’t it only used in emergencies?

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0 is “unless absolutely necessary”, 100 is “instantly”.

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Yes, and that’s the point. The only time swap is needed is during upgrades.

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6 posts were split to a new topic: Can swap file cause delays?

After running Jeff’s command to create the swap file, do I need to shutdown my server or something to make it work?

I did a git pull and rebuild app just to make sure it was all good. Not sure if it was necessary anyway.

Do I need to execute a shutdown as well? What would be the commands for that?

Also, is there any command I can run to make sure the swap file is working properly?

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The swapon command turns on the swap file (Jeff’s notes say “activate”). You don’t need to reboot (you could use sudo reboot to reboot if you wanted to for some other reason).

free will give you memory info, including swap.

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Oh I see. Great. No need to reboot then. Swap seems fine then:

Thanks for the info!

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Ran into Errno::ENOMEM: Cannot allocate memory and https://meta.discourse.org/t/cannot-allocate-memory-during-upgrade/27619?u=balupton so tried this, but got:

root@bevry-discourse-ubuntu-1gb-sgp1:~# sudo install -o root -g root -m 0600 /dev/null /swapfile
install: cannot remove ‘/swapfile’: Operation not permitted
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Do you have swap on already?

free will show you swap.

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Anyone have any advice on if I need a swapfile if my server has 4GB of memory? If so, what should the size be?

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You are not required to. If you wanted to play it safe, a 1 GB file should be more than sufficient and rarely used.

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Hello ,

There is any sense to create 3 GB , 4GB SWAP for instance with 1 GB RAM . Any profits here ?(1% more better work is a profit )

You are better off investing in more physical RAM than a larger SWAP file.

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Obviously you can create a swapfile any size you want. If it is not needed, it will just sit there merrily holding zeros. The disk space will simply be wasted.

So the trick is to size your swap large enough for the heaviest operation, which in Discourse should be the rebuild. Check memory usage on a rebuild to see how much is needed.

I think there are studies out there saying that very large swap files will not be useful because the CPU is gonna start thrashing way before that much swap is used.

EDIT: Searching on the net, it is recommended the swap to be no larger than 2 times physical RAM due to declining returns of adding more.

./discourse-setup will now create the swap file, so there is (usually) no reason to do it yourself. If you have a too-small swapfile you should delete it before running discourse-setup.

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