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Re: [PATCH for-4.2 1/4] Revert "qcow2: skip writing zero buffers to empt
Re: [PATCH for-4.2 1/4] Revert "qcow2: skip writing zero buffers to empty COW areas"
Fri, 1 Nov 2019 15:01:02 +0100
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On 01.11.19 13:40, Eric Blake wrote:
> On 11/1/19 11:00 AM, Max Reitz wrote:
>> This reverts commit c8bb23cbdbe32f5c326365e0a82e1b0e68cdcd8a.
>> This commit causes fundamental performance problems on XFS (because
>> fallocate() stalls the AIO pipeline), and as such it is not clear that
>> we should unconditionally enable this behavior.
>> We expect subclusters to alleviate the performance penalty of small
>> writes to newly allocated clusters, so when we get them, the originally
>> intended performance gain may actually no longer be significant.
>> If we want to reintroduce something similar to c8bb23cbdbe, it will
>> require extensive benchmarking on various systems with subclusters
>> Cc: address@hidden
>> Signed-off-by: Max Reitz <address@hidden>
>> +++ b/qapi/block-core.json
>> @@ -3304,8 +3304,6 @@
>> # @cor_write: a write due to copy-on-read (since 2.11)
>> -# @cluster_alloc_space: an allocation of file space for a cluster
>> (since 4.1)
>> # @none: triggers once at creation of the blkdebug node (since 4.1)
> Deleting released qapi is not backwards-compatible.
I’ll just not make changes to the QAPI schema. It doesn’t hurt to leave
> However, given that
> the only known user of this interface is debug testing via iotests, I'm
> not too concerned that we would be impacting any external users.
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[PATCH for-4.2 2/4] block: Make wait/mark serialising requests public, Max Reitz, 2019/11/01
[PATCH for-4.2 3/4] block: Add bdrv_co_get_self_request(), Max Reitz, 2019/11/01
[PATCH for-4.2 4/4] block/file-posix: Let post-EOF fallocate serialize, Max Reitz, 2019/11/01
Re: [PATCH for-4.2 0/4] qcow2: Fix data corruption on XFS, Max Reitz, 2019/11/01