Re: swap on zram service unit, using Conflicts=umount

[Lennart Poettering <lennart@xxxxxxxxxxxxxx>]

On Sa, 22.06.19 10:42, Chris Murphy (lists@xxxxxxxxxxxxxxxxx) wrote:

> Hi,
>
> I've got a commit to add 'Conflicts=umount.target' to this zram
> service based on a bug comment I cited in the comment. But I'm not
> certain I understand if it's a good idea or necessary.
>
> https://src.fedoraproject.org/fork/chrismurphy/rpms/zram/c/63900c455e8a53827aed697b9f602709b7897eb2?branch=devel
>
> I figure it's plausible at shutdown time that something is swapped
> out, and a umount before swapoff could hang (briefly or indefinitely I
> don't know), and therefore it's probably better to cause swapoff to
> happen before umount.

So for tmpfs mounts that don't turn off DefaultDependencies= we
implicit add in an After=swap.target ordering dep. The thinking was
that there's no point in swapping in all data of a tmpfs because we
want to detach the swap device when we are going to flush it all out
right after anyway. This made quite a difference to some folks.

That said, I don't really grok zram, and not sure why there's any need
to detach it at all. I mean, if at shutdown we lose compressed RAM
or lose uncompressed RAM shouldn't really matter. Hence from my
perspective there's no need for Conflicts= at all, but maybe I am
missing something?

Zbigniew, any particular reason why you added the Conflicts= line?

Lennart

--
Lennart Poettering, Berlin
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