Re: Adding file swap on btrfs

[Jonathan Billings <billings@xxxxxxxxxx>]

On Dec 19, 2022, at 14:59, Neal Becker <ndbecker2@xxxxxxxxx> wrote:

I've just installed f37 on a new lenovo x1 carbon.

One thing, the installation didn't setup any swap (other than zswap).

After a bit of reading I found

sudo btrfs filesystem mkswapfile -s 32G /swapfile

But:

 sudo swapon -v /swapfile
swapon: /swapfile: found signature [pagesize=4096, signature=swap]
swapon: /swapfile: pagesize=4096, swapsize=1073741824, devsize=34359738368

Although I created 32G swapfile, only 1G is used.

swapon
NAME       TYPE       SIZE USED PRIO
/dev/zram0 partition    8G 6.3M  100
/swapfile  file      1024M   0B   -2

What's wrong?

This is pretty much expected behavior. 

Your zram swap device has a priority of 100, the swap file of -2. 

See the swap(2) man page:

https://linux.die.net/man/2/swapon

Basically, you want to have swapped pages in the compressed memory device, it is much faster and essentially is expanding available RAM. If memory pressure gets high enough it will use your swap file, but unlikely unless your system is really thrashing. 

--

Jonathan Billings

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