Re: hibernation/snapshot design [was Re: [PATCH] Remove processfreezer from suspend to RAM pathway]

From: david
Date: Sun Jul 08 2007 - 19:25:08 EST

On Mon, 9 Jul 2007, Pavel Machek wrote:

Actaully, I'm perfectly fine with that, as long as each task blocked by
the
driver due to suspend has PF_FROZEN (or something similar) set. Then, at
least theoretically, we'll be able to drop the freezer from the suspend
code
path and move it after device_suspend() (or the hibernation-specific
equivalent) for hibernation (in that case there shouldn't be a problem
with
any task waiting on I/O while the freezer is running ;-)).

I don't see the need for a freezer for snapshot but that's a different
issue. (stop_machine looks good enough to me).

Freezer is not needed for snapshot -- it is needed so that we can
write out the snapshot to disk without the need for special
drivers/block/simple-ide-for-suspend.c. (We are doing snapshot, then
write to disk from userland code in uswsusp).

instead of trying to freeze most of the system, could you do something
like start a virtual machine sandbox to write the data out, and not let
any userspace other then the sandbox operate?

you would need to throw away disk buffers so that you don't mix current
pending I/O with I/O from the sandbox, and this would be a visable change
for how suspend is setup, but wouldn't this work?

It feels kind of expensive, but yes, we could use another kernel for
doing the dump. Kdump people are using that. We could use hypervisor
for doing the dump. Xen people are doing that. (But I do not think any
of those solutions is suitable for "lets hibernate my notebook" case).

expensive and reliable beats efficiant and unrelaible.

why do you say that neither would work for the "lets hibernate my notebook" case?

David Lang
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