[ovirt-devel] VDSM changes Linux memory dirty ratios - why?

[Martin Polednik]

On 30/11/16 13:11 +0100, Sven Kieske wrote:
>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!).
>>
>> Partially unrelated - the trend today is actually to put NOOP on the VMs -
>> the deadline is quite meaningless, as the host scheduler will reschedule
>> 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.
>>
>> In short, I think it's an outdated decision that perhaps should be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.

Current values seem to be optimal; considering this use case I'd
definitely leave it in place.

>-- 
>Mit freundlichen Grüßen / Regards
>
>Sven Kieske
>
>Systemadministrator
>Mittwald CM Service GmbH & Co. KG
>Königsberger Straße 6
>32339 Espelkamp
>T: +495772 293100
>F: +495772 293333
>https://www.mittwald.de
>Geschäftsführer: Robert Meyer
>St.Nr.: 331/5721/1033, USt-IdNr.: DE814773217, HRA 6640, AG Bad Oeynhausen
>Komplementärin: Robert Meyer Verwaltungs GmbH, HRB 13260, AG Bad Oeynhausen
>




>_______________________________________________
>Devel mailing list
>Devel at ovirt.org
>http://lists.ovirt.org/mailman/listinfo/devel