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Re: [PATCH v3 04/10] hbitmap: drop meta bitmaps as they are unused

From: Eric Blake
Subject: Re: [PATCH v3 04/10] hbitmap: drop meta bitmaps as they are unused
Date: Mon, 20 Jan 2020 13:53:29 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.1

On 1/20/20 11:28 AM, Vladimir Sementsov-Ogievskiy wrote:

I'm a bit not follow what you mean. I can just note, that dirty-bitmap.c
part of meta bitmaps was recently removed, and hbitmap.c part I forgot to

Yes, but who used that dirty-bitmap.c interface?  As far as I can tell,

Yes, as far as I know, nobody and never.

Meta bitmaps were intended to control live migration of bitmaps and to
implement something like partial sync of bitmaps (write to qcow2 only
changed part of bitmap), but migration implemented in other way
(postcopy) and the second thing was not implemented.

OK.  I was wondering why they were implemented without ever having been
used (as far as I can tell).

It was too optimistic preparatory series.

Matches my recollection (we had several ideas about how to tackle it; meta-bitmaps was proposed as one idea and this code landed, but we never actually finished that idea before a better one was actually coded, so this has always been dead code).

(I can never finally understand, series - who a they or what is it?
   Plural or singular?

English is funny; "series" is one of the few words that works as both singular and plural (another example is "sheep").

They were too optimistic series? Sounds weird..

My spin: "The original series was too optimistic."

   And if one series is series, than what about several serieses?
   OK, let's say, it was too optimistic preparatory patch set :)

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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