Re: Hibernate/Resume and dm-cache, dm-writeboost...

[Joe Thornber <thornber@redhat.com>]

On Wed, Dec 24, 2014 at 07:35:49PM +0100, Rolf Fokkens wrote:
> Hi all,
> 
> On the linux-bcache mailing list the potential issue was brought up
> about writes to backing or caching device after bringing up devices
> in initramdisk, but prior to an actual resume. The actual issue is
> that there should be no writes between hibernation and resume:
> 
> http://www.spinics.net/lists/linux-bcache/msg02692.html
> 
> If this is an issue for bcache, I can imagine it also is for other
> caching solutions like dm-cache and dm-writeboost. I'm not an expert
> on this, but from my user perspective it seems somewhat concerning
> (for both bcache and the DM caching solutions) and an expert view on
> this might be needed.

Thanks for bringing this to our attention.  I think dm-cache provides
the neccessary tools to do this; either setting the migration
threshold to zero, or switch to write through mode for the duration of
the hibernate.  But atm this would need to be triggered from userland.
I need to look at hibernate more.

- Joe