Fix disable swap failed in Centos/RHEL 7

[yankay]

What type of PR is this?

/kind bug

What this PR does / why we need it:

After #10587 , the swap cannot be disabled in Centos/RHEL 7.
After some investigating, the swap cannot be disabled by systemctl mask swap.target in this os. And it should be disabled by modify the /etc/fstab according to https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/storage_administration_guide/s1-swap-removing

Which issue(s) this PR fixes:

Fixes #10741
Fixes #10581

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

Fix disable swap failed in Centos/RHEL 7

[k8s-ci-robot]

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[VannTen]

After some investigating, the swap cannot be disabled by systemctl mask swap.target in this os

Did you find out which version of systemd changed that ?
I found systemd/systemd@90060fa which could have explained that kind of thing but the reported version in #10741 should have it as well. I'm gonna ask on systemd mailing list if they have idea.

[yankay]

After some investigating, the swap cannot be disabled by systemctl mask swap.target in this os

Did you find out which version of systemd changed that ? I found systemd/systemd@90060fa which could have explained that kind of thing but the reported version in #10741 should have it as well. I'm gonna ask on systemd mailing list if they have idea.

Hi @VannTen

The systemds version is 219.

[root@kay18x ~]# cat /etc/os-release
NAME="CentOS Linux"
VERSION="7 (Core)"

[root@kay18x ~]# uname -r
3.10.0-1160.el7.x86_64

[root@kay18x ~]# systemctl --version
systemd 219

Because the Centos 7 is still widely used, the swap disable is important to Kubernetes.
And the PR can also fix the #10581 ,

Would you please give a lgtm to this PR :-)

[VannTen]

/lgtm
For future ref for myself, the root cause:
It looks like .device units backing .swap units automatically get a Wants on the swap unit, not sure why (unless I missed a SYSTEMD_WANTS udev property on the blocks).

Happens with lvm, but probably without it as well.

[yankay]

/lgtm For future ref for myself, the root cause: It looks like .device units backing .swap units automatically get a Wants on the swap unit, not sure why (unless I missed a SYSTEMD_WANTS udev property on the blocks).

Happens with lvm, but probably without it as well.

@VannTen , Thank you for the PR review :-)