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Re: [Qemu-block] [Qemu-devel] [PATCH 4/4] block/qcow2: add zlib-fast com
From: |
Daniel P. Berrange |
Subject: |
Re: [Qemu-block] [Qemu-devel] [PATCH 4/4] block/qcow2: add zlib-fast compression algorithm |
Date: |
Tue, 27 Jun 2017 14:16:05 +0100 |
User-agent: |
Mutt/1.8.0 (2017-02-23) |
On Tue, Jun 27, 2017 at 02:34:10PM +0200, Peter Lieven wrote:
> this adds support for optimized zlib settings which almost
> tripples the compression speed while maintaining about
> the same compressed size.
>
> Signed-off-by: Peter Lieven <address@hidden>
> ---
> block/qcow2-cluster.c | 3 ++-
> block/qcow2.c | 11 +++++++++--
> block/qcow2.h | 1 +
> qemu-img.texi | 1 +
> 4 files changed, 13 insertions(+), 3 deletions(-)
> diff --git a/qemu-img.texi b/qemu-img.texi
> index 043c1ba..83a5db2 100644
> --- a/qemu-img.texi
> +++ b/qemu-img.texi
> @@ -627,6 +627,7 @@ The following options are available if support for the
> respective libraries
> has been enabled at compile time:
>
> zlib Uses standard zlib compression (default)
> + zlib-fast Uses zlib compression with optimized compression
> parameters
This looks like a poor design from a future proofing POV. I would much
rather see us introduce a more flexible modelling of compression at the
QAPI layer which lets us have tunables for each algorith, in the same
way that the qcow2 built-in encryption now has ability to set tunables
for each algorithm.
eg your "zlib-fast" impl which just uses zlib with a window size of -15
could be expressed as
qemu-img create -o compress.format=zlib,compress.window=-15
> lzo Uses LZO1X compression
Regards,
Daniel
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