On 6/5/20 7:33 PM, Chris Murphy wrote:
On Fri, Jun 5, 2020 at 8:12 PM Samuel Sieb <samuel@xxxxxxxx> wrote:
All three of those listed provide competing configurations for swap on
zram. Just to make a fine point, zram is generic, it is not swap
specific. It's just a compressed ram disk. Zswap is a different thing,
it is swap specific, providing a memory based writeback cache to a
disk based swap.
Ok, that makes sense about zram. It's a lot simpler than I was thinking
it was.
The generator does require a reboot to change configurations. You
could absolutely say, but Chris, the other ones you can just systemctl
restart! That is true, but except for testing, I don't see that as an
advantage compared to the overall simplisticity of zram-generator and
reusing the existing infrastructure in systemd that's already well
tested and maintained.
Sure, I'll set that up for the next time I reboot. But that is likely
to still be a long time from now.
Although really any value higher than the disk based swap is sufficient.
The systemd-swap service appears to set the priority of zram to the
maximum possible.
No, it was quite clear that I was modifying the right config. It's the
/etc/systemd/swap.conf as described in the man page and it was affecting
the result.
OK that is not for zram-generator. That's for one of the others. Off
hand I don't know which one it's for, this is way too confusing
because of all the competing implementations, which is part of the
motivation of the feature -> buh bye, thank you for your service!
Sorry, I guess that wasn't clear. That's the config file for
systemd-swap which is what I was testing.
Part of my concern is that if it's not actually full, then why is it
using so much of the disk swap?
Not sure. What should be true is if you swapoff on /dev/sda3 it'll
move any referenced anon pages to /dev/zram0. And then if you swapon
/dev/sda3 it will use 0 bytes until /dev/zram0 is full. What kernel
version are you using?
That is what I did do.
kernel 5.5.17-200.fc31.x86_64
For upstream, do you mean the kernel?
Yes. bugzilla.kernel.org - this goes to the linux-mm folks (memory
management) but you can search for a zram bug and just see what
component they use and post the bug here and I'll pick it up.
I reset everything and now I can't reproduce it. I wonder if it was
because I had zswap enabled as well. When I was going to file the bug
report, I came across a comment that it's not beneficial to use them
both at the same time.
# swapon
NAME TYPE SIZE USED PRIO
/dev/sda3 partition 16G 0B -2
/zram0 partition 5G 4.6G 32767
# zramctl
NAME ALGORITHM DISKSIZE DATA COMPR TOTAL STREAMS MOUNTPOINT
/dev/zram0 lz4 5G 4.6G 1.5G 1.5G 4
It looks like it's working properly now. So it seems likely that it was
user error. And for the little it matters, I approve of the change
proposal. I will have to test it out on my other systems as well now.
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