Fedora reawakens the hibernation debate [LWN.net]

Fedora reawakens the hibernation debate

Posted Oct 9, 2018 17:12 UTC (Tue) by Cyberax (✭ supporter ✭, #52523)
In reply to: Fedora reawakens the hibernation debate by mcortese
Parent article: Fedora reawakens the hibernation debate

If root is a non-clean state then you can’t use it for resume anyway, so no problem here.

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Fedora reawakens the hibernation debate

Posted Oct 11, 2018 21:17 UTC (Thu) by mcortese (guest, #52099) [Link] (2 responses)

> If root is a non-clean state then you can’t use it for resume anyway, so no problem here

Why? At any time the fs on disk can be non-clean while the vfs has pending changes not landed on disk yet. If the system is suspended in that moment, it's frozen in that precise state. If it's then hibernated, that state is written to swap.

For resume to work in such case, neither the kernel nor the initramfs must reside in the root fs.

This is just an example of the several conditions systemd should check before asserting that the system is ready for hibernation. Now, after reading the whole Fedora thread, I understand that systemd does nothing more than checking if the free swap is equal or greater than the used RAM. So when it says "CanHibernate" it actually means: this system *could* be configured to hibernate but I have no idea if it really is.

My opinion is that GNOME should not silently default to use hibernation only based on systemd's CanHibernate flag.

Fedora reawakens the hibernation debate

Posted Oct 11, 2018 21:21 UTC (Thu) by Cyberax (✭ supporter ✭, #52523) [Link] (1 responses)

As a part of the hibernation process the pending writes are flushed and the IO is quiesced. So if you have a dirty FS then you can be sure that it's not been used for hibernation.

Fedora reawakens the hibernation debate

Posted Oct 13, 2018 19:18 UTC (Sat) by mcortese (guest, #52099) [Link]

I didn't know that. Thanks for pointing it out.

So, while suspend & resume is nearly transparent for the running processes, hibernate & resume heavily changes the system's internal state.

I wonder if hibernation can stall in case of big IO backlog?