1:11 p.m.
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From: Sven Kieske <s.kieske(a)mittwald.de>
To: devel(a)ovirt.org
Message-ID: <11712170-1758-96b5-adb8-eb29d59be1b8(a)mittwald.de>
Subject: Re: [ovirt-devel] VDSM changes Linux memory dirty ratios - why?
References: <CAJgorsbMk1UeLt82GOWsVKOmj=Kse+4CvhoT2E_kj=PUnhG28A(a)mail.gmail.com>
<20161130074847.GA1215(a)dhcp130-218.brq.redhat.com>
<CAJgorsYqRX84st-jByqVbaUHCX=TmtnQeXw1=6FPu_Mbz6kUzg(a)mail.gmail.com>
In-Reply-To: <CAJgorsYqRX84st-jByqVbaUHCX=TmtnQeXw1=6FPu_Mbz6kUzg(a)mail.gmail.com>
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On 30/11/16 09:13, Yaniv Kaul wrote:
Thanks, but it really makes no sense to me. The direct IO by the VMs
is=
going to a different storage than what the host is writing to, in
most
cases.
The host would write to the local disk, the VMs - to a shared storage,
across NFS or block layer or so. Moreover, their IO is not buffered.
There is very little IO coming from the host itself, generally (I hope
so!).
=20
Partially unrelated - the trend today is actually to put NOOP on the VM=
s -
the deadline is quite meaningless, as the host scheduler will
reschedul=
e
anyway as it see fits.
Most likely it is also a deadline scheduler (but could be NOOP as well =
if
it's an all flash array, for example). Therefore there is no
reason for=
anything but simple NOOP on the VMs themselves.
=20
In short, I think it's an outdated decision that perhaps should be
revisited. Not urgent, though.
Y.
I know it's not the most cared about usecase
but I'd like to add that this might affect local storage
domains, which I happen to use a lot, and maybe others too.
--=20
Mit freundlichen Gr=FC=DFen / Regards
Sven Kieske
Systemadministrator
Mittwald CM Service GmbH & Co. KG
K=F6nigsberger Stra=DFe 6
32339 Espelkamp
T: +495772 293100
F: +495772 293333
https://www.mittwald.de
Gesch=E4ftsf=FChrer: Robert Meyer
St.Nr.: 331/5721/1033, USt-IdNr.: DE814773217, HRA 6640, AG Bad Oeynhause=
n
Komplement=E4rin: Robert Meyer Verwaltungs GmbH, HRB 13260, AG Bad Oeynha=
usen
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