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

From: Michael S. Tsirkin
Subject: Re: [Qemu-devel] [PATCH v2] migration: skip sending ram pages released by virtio-balloon driver.
Date: Wed, 13 Apr 2016 14:10:32 +0300

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 ...

> and use 
> current patch set to support other remaining protocols?

Even disregarding postcopy, I think there were
comments that need to be addressed.


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