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Re: [Qemu-devel] [PATCH v12 0/6] qcow2, raw: add preallocation=full and


From: Richard W.M. Jones
Subject: Re: [Qemu-devel] [PATCH v12 0/6] qcow2, raw: add preallocation=full and preallocation=falloc
Date: Mon, 25 Aug 2014 14:44:52 +0100
User-agent: Mutt/1.5.20 (2009-12-10)

On Mon, Aug 25, 2014 at 01:18:30PM +0800, Hu Tao wrote:
> What if user cares about time(writing zeroes or non-zeroes is
> time-consuming) and wants falloc only sometimes? I think this is the
> main difference between preallocation=falloc and preallocation=full.

Also posix_fallocate in glibc falls back to writing zeroes when the
kernel/VFS doesn't support a true fallocate.  So I'm afraid your patch
5/6 has a slow path, at least on common Linux distros.

Rich.

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