On Wed, 2006-06-21 at 08:08 -0700, Linus Torvalds wrote: > > 4-driver thaw, subsystems stay frozen (that is VM, filesystems, > > userland) > > Yes and no. We might actually want to thaw some subsystems too. > > Obviously, there's no reason to thaw user programs (even if you could > wake them up, they couldn't be allowed to make any forward progress that > is "visible"), but once you have snapshotted things, you might actually be > better off allowing a fair amount of "normal" operations. As long as you don't go anywhere near persistant storage like filesystems... Might be worth having a global ro remount as part of preparing subsystems.... > For example, you might decide that you want to actually _kill_ all user > processes at that point, and allow kernel processes that you wanted > quiescent for snapshotting to thaw. Once you have built the snapshot > image, many of the reasons to freeze are gone - not just for drivers. Ok. > At that point, the only thing you want to make sure of is that nobody > writes to swap any more, and doesn't write to the filesystem (or network, > for that matter). > > > 5-shutdown or driver suspend S4 > > Not yet. > > 5 - write snapshot to disk > > Because ytou need to do that after the thaw, of course. Yes, sure, that one was so obvious that I forgot about it :) > And only _then_ do you actually shutdown or do S4. Yup. > > The only little possible issue there is that the subsystems being still > > stopped, some drivers may need to have a hard time doing 5 if they need > > to send requests to their own hardware for things like hard disk > > spindown, and they happen to use the block layer request queue for that > > (pumping device specific requests into it). > > I'd wake up all kernel daemons after snapshotting. There's no reason not > to, really (kswapd might be a special case, but quite frankly, I think > we're better off "turning off swap" than necessarily turning off kswapd > itself - ie again, the appropriate level to make sure swap doesn't get > dirtied afterwards is likely _higher_ up than the level that actually > makes the IO itself happen). Beware with things like knfsd trying to hit your filesystems too ... Ben.
