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Mon, 14 Sep 2020 17:32:04 +0000 (UTC) Date: Mon, 14 Sep 2020 18:32:01 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Nir Soffer Subject: Re: [PATCH 2/2] block: file-posix: Replace posix_fallocate with fallocate Message-ID: <20200914173201.GR1252186@redhat.com> References: <20200831140127.657134-1-nsoffer@redhat.com> <20200831140127.657134-3-nsoffer@redhat.com> MIME-Version: 1.0 In-Reply-To: <20200831140127.657134-3-nsoffer@redhat.com> User-Agent: Mutt/1.14.6 (2020-07-11) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0.001 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Disposition: inline Received-SPF: pass client-ip=205.139.110.61; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/14 02:33:07 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -38 X-Spam_score: -3.9 X-Spam_bar: --- X-Spam_report: (-3.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.792, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Kevin Wolf , qemu-block@nongnu.org, Markus Armbruster , qemu-devel@nongnu.org, Max Reitz , Nir Soffer Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Aug 31, 2020 at 05:01:27PM +0300, Nir Soffer wrote: > If fallocate() is not supported, posix_fallocate() falls back to > inefficient allocation, writing one byte for every 4k bytes[1]. This is > very slow compared with writing zeros. In oVirt we measured ~400% > improvement in allocation time when replacing posix_fallocate() with > manually writing zeroes[2]. > > We also know that posix_fallocated() does not work well when using OFD > locks[3]. We don't know the reason yet for this issue yet. > > Change preallocate_falloc() to use fallocate() instead of > posix_falloate(), and fall back to full preallocation if not supported. > > Here are quick test results with this change. > > Before (qemu-img-5.1.0-2.fc32.x86_64): > > $ time qemu-img create -f raw -o preallocation=falloc /tmp/nfs3/test.raw 6g > Formatting '/tmp/nfs3/test.raw', fmt=raw size=6442450944 preallocation=falloc > > real 0m42.100s > user 0m0.602s > sys 0m4.137s > > NFS stats: > calls      retrans    authrefrsh write > 1571583    0          1572205 1571321 > > After: > > $ time ./qemu-img create -f raw -o preallocation=falloc /tmp/nfs3/test.raw 6g > Formatting '/tmp/nfs3/test.raw', fmt=raw size=6442450944 preallocation=falloc > > real 0m15.551s > user 0m0.070s > sys 0m2.623s > > NFS stats: > calls      retrans    authrefrsh write > 24620      0          24624 24567   > > [1] https://code.woboq.org/userspace/glibc/sysdeps/posix/posix_fallocate.c.html#96 > [2] https://bugzilla.redhat.com/1850267#c25 > [3] https://bugzilla.redhat.com/1851097 This bug appears to be private to RH employees only, so rather than link to it, please summarize any important facts in it for benefit of nonn-RH QEMU contributors. > > Signed-off-by: Nir Soffer > --- > block/file-posix.c | 32 +++++++++----------------- > docs/system/qemu-block-drivers.rst.inc | 11 +++++---- > docs/tools/qemu-img.rst | 11 +++++---- > qapi/block-core.json | 4 ++-- > 4 files changed, 25 insertions(+), 33 deletions(-) Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|