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Re: [Qemu-devel] [PATCH v3 0/8] eliminate data write in bdrv_write_zeroe


From: Denis V. Lunev
Subject: Re: [Qemu-devel] [PATCH v3 0/8] eliminate data write in bdrv_write_zeroes on Linux in raw-posix.c
Date: Tue, 30 Dec 2014 14:07:37 +0300
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:24.0) Gecko/20100101 Thunderbird/24.6.0

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)



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