Re: What can OpenVZ do?

On Tue, Feb 17, 2009 at 04:40:39PM -0800, Dave Hansen wrote:

On Wed, 2009-02-18 at 01:32 +0100, Ingo Molnar wrote:

quoted

quoted

quoted

Uncheckpointable should be a one-way flag anyway. We want this 
to become usable, so uncheckpointable functionality should be as 
painful as possible, to make sure it's getting fixed ...

Again, as these patches stand, we don't support checkpointing 
when non-simple files are opened.  Basically, if a 
open()/lseek() pair won't get you back where you were, we 
don't deal with them.

init does non-checkpointable things.  If the flag is a one-way 
trip, we'll never be able to checkpoint because we'll always 
inherit init's ! checkpointable flag.

To fix this, we could start working on making sure we can 
checkpoint init, but that's practically worthless.

i mean, it should be per process (per app) one-way flag of 
course. If the app does something unsupported, it gets 
non-checkpointable and that's it.

OK, we can definitely do that.  Do you think it is OK to run through a
set of checks at exec() time to check if the app currently has any
unsupported things going on?  If we don't directly inherit the parent's
status, then we need to have *some* time when we check it.

Uncheckpointable is not one-way.

Imagine remap_file_pages(2) is unsupported. Now app uses
remap_file_pages(2), then unmaps interesting VMA. Now app is
checkpointable again.

As for overloading LSM, I think, it would be horrible.
Most hooks are useless, there are config options expanding LSM hooks,
and CPT and LSM are just totally orthogonal.

Instead, just (no offence) get big enough coverage -- run modern and
past distros, run servers packaged with them, and if you can checkpoint
all of this, you're mostly fine.

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