From: Eric Blake <eblake@redhat.com>
To: Kevin Wolf <kwolf@redhat.com>
Cc: famz@redhat.com, qemu-block@nongnu.org, qemu-devel@nongnu.org,
mreitz@redhat.com, Nir Soffer <nsoffer@redhat.com>,
pbonzini@redhat.com
Subject: Re: [Qemu-devel] [PATCH for-3.0] file-posix: Fix write_zeroes with unmap on block devices
Date: Thu, 26 Jul 2018 13:24:49 -0500 [thread overview]
Message-ID: <1d5a5355-344e-7029-f7d7-ddb52c65651a@redhat.com> (raw)
In-Reply-To: <6cdde651-acdc-e6eb-63fc-e7efe8136710@redhat.com>
On 07/26/2018 10:23 AM, Eric Blake wrote:
>
> Hmm - that thread also mentions FALLOC_FL_NO_HIDE_STALE, which is a new
> flag not present/documented on Fedora 28. I wonder if it helps, too.
Even more odd - that flag has been proposed to the kernel since 2012 but
still not mentioned in the F28 man page:
https://lwn.net/Articles/492920/
and that its use on block devices is much more recent, just last month:
https://webcache.googleusercontent.com/search?q=cache:1LV2Y06XnjkJ:https://patchwork.kernel.org/patch/10466183/+&cd=5&hl=en&ct=clnk&gl=us&client=firefox-b-1
but now that I've read that, it makes total sense that the combination
PUNCH_HOLE|NO_HIDE_STALE is explicitly asking for semantics of "discard
as fast as possible regardless of whatever later reads will see", while
plain PUNCH_HOLE means "guarantee that I can read zeroes, using the
fastest means possible [discard, if that works]"
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
next prev parent reply other threads:[~2018-07-26 18:24 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-26 11:33 [Qemu-devel] [PATCH for-3.0] file-posix: Fix write_zeroes with unmap on block devices Kevin Wolf
2018-07-26 14:28 ` Eric Blake
2018-07-26 15:06 ` [Qemu-devel] [Qemu-block] " Nir Soffer
2018-07-26 15:06 ` [Qemu-devel] " Kevin Wolf
2018-07-26 15:23 ` Eric Blake
2018-07-26 15:33 ` Kevin Wolf
2018-07-26 16:10 ` Eric Blake
2018-07-26 16:46 ` Nir Soffer
2018-07-26 16:58 ` Kevin Wolf
2018-07-26 17:34 ` Nir Soffer
2018-07-26 18:00 ` Eric Blake
2018-07-26 18:09 ` Kevin Wolf
2018-07-26 18:24 ` Eric Blake [this message]
2018-07-26 16:22 ` [Qemu-devel] [Qemu-block] " Nir Soffer
2018-07-26 16:41 ` Kevin Wolf
2018-07-26 16:54 ` Nir Soffer
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