Re: [Qemu-devel] [PATCH v4 0/9] Make 'dump-guest-memory' dump in kdump-compressed format

[Stefan Hajnoczi <stefanha@gmail.com>]

On Fri, Jun 28, 2013 at 10:57:28AM +0800, Qiao Nuohan wrote:
> On 06/27/2013 04:54 PM, Stefan Hajnoczi wrote:
> >
> >The interesting question is how effective this approach is.  If it's
> >good enough then it would be a fairly simple modification to dump.c.
> 
> I see, if excluding zero page in ELF can make a lot of size reduce, it's better
> to choose this method. But think over the situation that kernel is on for a
> long time, then few zero pages will be in memory, compression will do more work
> to reduce size not excluding zero pages. So the approach is not always
> effective.
> 
> A test on a 1GB memory, and the machine is just on:
> 
> size       format         method for reducing memory
> 
> 1.1GB      ELF            no
> 1.1GB      kdump          no
> 227MB      kdump          with all zero pages excluded
>  96MB      kdump          compressed with zero pages remained
>  88MB      kdump          compressed with zero pages excluded
> 
> excluding zero pages does some work, but compression seems to be more effective.
[...]
> >If it makes the code simpler and smaller it would be nice.
> 
> That's the point. I will make the code simpler.

I'm now convinced that kdump is worthwhile, thanks for providing data.

It would be nice to see the flattened kdump approach.

Stefan