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Date: Tue, 30 Dec 2014 14:07:37 +0300
From: "Denis V. Lunev" <den@openvz.org>
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Subject: Re: [Qemu-devel] [PATCH v3 0/8] eliminate data write in
 bdrv_write_zeroes on Linux in raw-posix.c
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To: Peter Lieven <pl@kamp.de>
Cc: Kevin Wolf <kwolf@redhat.com>, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>

On 30/12/14 13:55, Peter Lieven wrote:
> Am 30.12.2014 um 10:20 schrieb Denis V. Lunev:
>> These patches eliminate data writes completely on Linux if fallocate
>> FALLOC_FL_ZERO_RANGE or FALLOC_FL_PUNCH_HOLE are  supported on
>> underlying filesystem.
>>
>> I have performed several tests with non-aligned fallocate calls and
>> in all cases (with non-aligned fallocates) Linux performs fine, i.e.
>> areas are zeroed correctly. Checks were made on
>>     Linux 3.16.0-28-generic #38-Ubuntu SMP
>>
>> This should seriously increase performance in some special cases.
> Could you give a hint what that special cases are? It would help
> to evaluate and test the performance difference.
>
> Thanks,
> Peter

- 15% in Parallels Image expansion, see my side patchset
- writing zeroes to raw image with BLOCKDEV_DETECT_ZEROES_OPTIONS_ON set
    (actually I have kludged raw-posix.c to have this flag always set
    to perform independent testing)