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Re: [Qemu-devel] [PATCH v1 04/13] qcow2: preallocation at image expand


From: Eric Blake
Subject: Re: [Qemu-devel] [PATCH v1 04/13] qcow2: preallocation at image expand
Date: Mon, 22 May 2017 14:29:53 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.0

On 05/19/2017 04:34 AM, Anton Nefedov wrote:
> From: "Denis V. Lunev" <address@hidden>
> 
> This patch adds image preallocation at expand to provide better locality
> of QCOW2 image file and optimize this procedure for some distributed
> storages where this procedure is slow.
> 
> Image expand requests have to be suspended until the allocation is
> performed which is done via special QCowL2Meta.
> This meta is invisible to handle_dependencies() code.
> This is the main reason for also calling preallocation before metadata
> write: it might intersect with preallocation triggered by another IO,
> and has to yield

How does this interact with Max's work on preallocated truncate?
https://lists.gnu.org/archive/html/qemu-devel/2017-04/msg00267.html

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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