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From Wido den Hollander <>
Subject Re: KVM Host overprovisioning
Date Mon, 11 Sep 2017 11:00:30 GMT

> Op 10 september 2017 om 8:37 schreef Ivan Kudryavtsev <>:
> Hello, community.
> During the last years Linux kernel got some interesting features like KSM,
> ZSWAP, ZRAM. Hardware also steps forward and we see Intel 3d xpoint,
> extremely fast SSD drives with m.2 and PCI-E interfaces.
> These facilities enable potentially interesting use of overcommited RAM for
> hosts. According to IBM's investigations Zswap with LZ4/ZBUD increases
> virtual RAM on 40%.
> I investigated current Apache CloudStack memory overcommitment capabilities
> and they mostly affect VM's RAM by utilizing ballooning and I think it's
> not what necessary to open new facilities. There are many cases which can
> utilize ZSWAP and fast swap devices to efficiently provision more RAM than
> presents.
> I suppose, CloudStack Agent for KVM can have configured parameter which
> "mangles" RAM reported. From the other hand it can be done by implemented
> host properties on server side. I tried manual increasing in host table:
> update host set ram=ram * 1.4 where id=1;
> and it seems until the next host stats update it works as expected. I think
> this workaround is useful, but it's better to have the function in core
> like standard.

Can't you set memory over provisioning on a cluster basis in the GUI? I thought you could.


> Let me know what you think about it, it might be I don't understand
> something and ACS already has it in place? I also would like to hear your
> thoughts on ZSWAP usage in practice.
> -- 
> With best regards, Ivan Kudryavtsev
> Bitworks Software, Ltd.
> Cell: +7-923-414-1515
> WWW: <>

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