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Re: [Qemu-devel] [PATCH v2] migration: skip sending ram pages released b

From: Dr. David Alan Gilbert
Subject: Re: [Qemu-devel] [PATCH v2] migration: skip sending ram pages released by virtio-balloon driver.
Date: Wed, 13 Apr 2016 12:15:38 +0100
User-agent: Mutt/1.5.24 (2015-08-30)

* Michael S. Tsirkin (address@hidden) wrote:
> On Wed, Apr 13, 2016 at 04:24:55PM +0530, Jitendra Kolhe wrote:
> > Can we extend support for post-copy in a different patch set?
> If the optimization does not *help* on some paths,
> that's fine. The issue is with adding extra code
> special-casing protocols:
> +    if (migrate_postcopy_ram()) {
> +        balloon_bitmap_disable_state = BALLOON_BITMAP_DISABLE_PERMANENT;
> +    }
> Generally when one sees that patchset breaks XYZ...
> the easy solution is "check for XYZ
> and disable the optimization". But do this enough times
> and the codebase becomes impossible to reason about.
>       why did migration become slower? oh it enabled
>       optimization A and that conflicts with optimization B ...

Hang on; this is getting all very complicated; I wouldn't start tieing
this thing up with postcopy yet.  Lets try and keep this simple for starters.


> > and use 
> > current patch set to support other remaining protocols?
> Even disregarding postcopy, I think there were
> comments that need to be addressed.
> -- 
Dr. David Alan Gilbert / address@hidden / Manchester, UK

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