From: Kevin Wolf <kwolf@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>,
qemu-devel@nongnu.org, qemu-block@nongnu.org, armbru@redhat.com,
eblake@redhat.com, mreitz@redhat.com, fam@euphon.net,
stefanha@redhat.com, den@openvz.org
Subject: Re: [Qemu-devel] [PATCH] file-posix: add rough-block-status parameter
Date: Wed, 9 Jan 2019 18:09:29 +0100 [thread overview]
Message-ID: <20190109170929.GJ4867@localhost.localdomain> (raw)
In-Reply-To: <61f6ac4d-91ab-f9cb-67e5-e0f5ce17524d@redhat.com>
Am 09.01.2019 um 17:55 hat Paolo Bonzini geschrieben:
> On 09/01/19 17:51, Kevin Wolf wrote:
> > Am 09.01.2019 um 17:42 hat Paolo Bonzini geschrieben:
> >> On 09/01/19 12:23, Kevin Wolf wrote:
> >>> Also note that this is only metadata preallocation; full preallocation
> >>> will still return allocated for the protocol layer and so it will always
> >>> be slow.
> >>
> >> Full preallocation these days can create images with preallocated but
> >> known-zero blocks, I think?
> >
> > That would defeat one of the main purposes of preallocation because it
> > would still require COW and metadata updates on the first write.
>
> Sorry I mean at the protocol level, like FALLOC_FL_ZERO_RANGE. It would
> still require metadata updates on the filesystem level, unlike "real"
> full preallocation, but no qcow2 metadata updates.
preallocation=full doesn't do that. preallocation=falloc is more like
it, though that is just posix_fallocate(), not FALLOC_FL_ZERO_RANGE. But
when called on a new file, it might result in the same thing? Not sure.
Kevin
next prev parent reply other threads:[~2019-01-09 17:09 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-08 19:45 [Qemu-devel] [PATCH] file-posix: add rough-block-status parameter Vladimir Sementsov-Ogievskiy
2019-01-08 20:11 ` Eric Blake
2019-01-09 11:23 ` Kevin Wolf
2019-01-09 16:42 ` Paolo Bonzini
2019-01-09 16:51 ` Kevin Wolf
2019-01-09 16:55 ` Paolo Bonzini
2019-01-09 17:09 ` Kevin Wolf [this message]
2019-01-09 18:09 ` Denis V.Lunev
2019-01-09 17:00 ` Eric Blake
2019-01-09 12:33 ` [Qemu-devel] [Qemu-block] " Stefan Hajnoczi
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