Date: Tue, 13 Feb 2018 10:06:59 -0800 (PST) From: "Rodney W. Grimes" <freebsd-rwg@pdx.rh.CN85.dnsmgr.net> To: tech-lists <tech-lists@zyxst.net> Cc: freebsd-virtualization@freebsd.org Subject: Re: bhyve and contention Message-ID: <201802131806.w1DI6xp7049909@pdx.rh.CN85.dnsmgr.net> In-Reply-To: <61adce39-e393-f533-3772-6503a72972af@zyxst.net>
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> Hello virtualizations, > > Please can anyone tell me what happens in the following scenarios: I can speculate on some of what may happen, this may not be exact, but should give you an idea. > 1. > freebsd-11 server, 5x freebsd-11 guests > The server has 32GB ram installed. it's an i7 so 8 cores. There's 64GB > swap. Each guest that bhyve loads is with m 8192M, so ram is > overcommitted by 6GB. 5 x 8G == 40G, 32G ram, so 8G overcommit, not 6. Further more you have base sytem memory which includes such things as kernel, page tables, loaded modules, buffer cache, possibly ZFS arc cache since you dont mention that. ZFS arc cache will attempt to grow to something like 95% of memory, so you can actually be in full 40G over commit situation on memory. > What happens to the guests and the server? Do either (or both) crash? Or > is there something in bhyve that will make memory allocated on a > best-effort basis? With 64G of swap space avaliable, and assuming your either not running ZFS or have limited zfs arc cache to say 2G or 4G the system should not crash. You however are in a memory overcommit and things are likely to be sluggish and may even appear crashed. Bhyve uses swap backed annonymous vm so the vm system shall apply best effort to meet the demands. Swapping vm guest memory pages though not idea does work, but as I said, things are going to get very sluggish both on the host and the guest. > 2. > In the following context, the server is the same but this time all five > guests have -c 4 per guest, so bhyve is asking 12 more cores than that > existing in hardware. Does the guest fail to load, do either guest or > server crash? The is core over commit, very common in the virtualization world, bhyve does its best effort to give the guests cores as needed. I am typing this on a system with a 4 core CPU (2 real x 2 thread) that is running 10 bhyve VM's, each just single core. My host load average is: 6:01PM up 3 days, 16:01, 7 users, load averages: 3.77, 3.34, 3.22 One of those guests is running a stable/10 make world in a memory contrained situation (512MB). The host system is responsive and working fine, as are the guests. I am fine with CPU over commit, but I watch the memory situation like a hawk. I only have 12GB of memory, I have restricted ZFS arc cache to 6G The sums of the memory of all the running VM's is about 2G This leaves me about 4G of fiddle around room on the host for occasional VM spin up, or other memory heavy things. I run all my VM's with the wired memory option. > > thanks, > -- > J. > _______________________________________________ > freebsd-virtualization@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-virtualization > To unsubscribe, send any mail to "freebsd-virtualization-unsubscribe@freebsd.org" > -- Rod Grimes rgrimes@freebsd.org
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