From: Peter Lieven <pl@kamp.de>
To: Kevin Wolf <kwolf@redhat.com>
Cc: qemu-devel@nongnu.org, qemu-block <qemu-block@nongnu.org>,
Max Reitz <mreitz@redhat.com>
Subject: Re: [RFC PATCH 0/2] qemu-img convert: Fix sparseness detection
Date: Mon, 19 Apr 2021 11:13:22 +0200 [thread overview]
Message-ID: <AD190B98-4F27-4170-94BE-D0E3DB2A3EB3@kamp.de> (raw)
In-Reply-To: <07747AB5-5BCE-49EE-A3AB-03AA7B6211F8@kamp.de>
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> Am 19.04.2021 um 10:36 schrieb Peter Lieven <pl@kamp.de>:
>
>
>
>> Am 15.04.2021 um 17:22 schrieb Kevin Wolf <kwolf@redhat.com>:
>>
>> Peter, three years ago you changed 'qemu-img convert' to sacrifice some
>> sparsification in order to get aligned requests on the target image. At
>> the time, I thought the impact would be small, but it turns out that
>> this can end up wasting gigabytes of storagee (like converting a fully
>> zeroed 10 GB image taking 2.8 GB instead of a few kilobytes).
>>
>> https://bugzilla.redhat.com/show_bug.cgi?id=1882917
>>
>> I'm not entirely sure how to attack this best since this is a tradeoff,
>> but maybe the approach in this series is still good enough for the case
>> that you wanted to fix back then?
>>
>> Of course, it would be possible to have a more complete fix like looking
>> forward a few blocks more before writing data, but that would probably
>> not be entirely trivial because you would have to merge blocks with ZERO
>> block status with DATA blocks that contain only zeros. I'm not sure if
>> it's worth this complication of the code.
>
> I will try to look into this asap.
Besides from the reproducer described in the ticket, I retried my old conversion test in our environment:
Before commit 8dcd3c9b91: reads 4608 writes 14959
After commit 8dcd3c9b91: reads 0 writes 14924
With Kevins patch: reads 110 writes 14924
I think this is a good result if it avoids other issues.
Peter
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next prev parent reply other threads:[~2021-04-19 9:15 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-15 15:22 [RFC PATCH 0/2] qemu-img convert: Fix sparseness detection Kevin Wolf
2021-04-15 15:22 ` [RFC PATCH 1/2] iotests: Test qemu-img convert of zeroed data cluster Kevin Wolf
2021-04-15 15:22 ` [RFC PATCH 2/2] qemu-img convert: Fix sparseness detection Kevin Wolf
2021-04-20 14:31 ` Vladimir Sementsov-Ogievskiy
2021-04-20 15:04 ` Kevin Wolf
2021-04-20 16:52 ` Vladimir Sementsov-Ogievskiy
2021-05-19 13:24 ` Peter Lieven
2021-05-19 16:48 ` Kevin Wolf
2021-12-03 11:17 ` Peter Lieven
2021-12-03 23:04 ` Vladimir Sementsov-Ogievskiy
2021-12-04 9:53 ` Peter Lieven
2021-12-17 14:43 ` Peter Lieven
2021-04-19 8:36 ` [RFC PATCH 0/2] " Peter Lieven
2021-04-19 9:13 ` Peter Lieven [this message]
2021-04-19 12:31 ` Kevin Wolf
2021-04-19 17:12 ` Peter Lieven
2021-04-20 6:49 ` Kevin Wolf
2021-04-19 11:22 ` Kevin Wolf
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