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Re: [PATCH v8 7/7] block: apply COR-filter to block-stream jobs

From: Max Reitz
Subject: Re: [PATCH v8 7/7] block: apply COR-filter to block-stream jobs
Date: Fri, 4 Sep 2020 15:41:49 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0

On 28.08.20 18:52, Andrey Shinkevich wrote:
> This patch completes the series with the COR-filter insertion for
> block-stream operations. Adding the filter makes it possible for copied
> regions to be discarded in backing files during the block-stream job,
> what will reduce the disk overuse.
> The COR-filter insertion incurs changes in the iotests case
> 245:test_block_stream_4 that reopens the backing chain during a
> block-stream job. There are changes in the iotests #030 as well.
> The iotests case 030:test_stream_parallel was deleted due to multiple
> conflicts between the concurrent job operations over the same backing
> chain. The base backing node for one job is the top node for another
> job. It may change due to the filter node inserted into the backing
> chain while both jobs are running. Another issue is that the parts of
> the backing chain are being frozen by the running job and may not be
> changed by the concurrent job when needed. The concept of the parallel
> jobs with common nodes is considered vital no more.
> Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
> ---
>  block/stream.c             | 78 
> +++++++++++++++++++++++++++-------------------
>  tests/qemu-iotests/030     | 50 +++--------------------------
>  tests/qemu-iotests/030.out |  4 +--
>  tests/qemu-iotests/245     | 19 ++++++++---
>  4 files changed, 67 insertions(+), 84 deletions(-)

I’m not sure I can really review this, when I don’t know what the COR
filter really does.  For example, as it is in this version, it
unconditionally performs COR, and so on guest reads will copy everything
from the bottom layers even when they are below the base node.


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