bradduane's Posts

Re: What happens to memory that is swapped to disk after RAM is freed?

by Contributor in ESXi Discussions
‎03-19-2014 12:57 PM
‎03-19-2014 12:57 PM
Based on this document here: http://pubs.vmware.com/vsphere-4-esx-vcenter/index.jsp?topic=/com.vmware.vsphere.resourcemanagement.doc_41/performance_monitoring_utilities_resxtop_and_esxtop/r_memor... See more...
Based on this document here: http://pubs.vmware.com/vsphere-4-esx-vcenter/index.jsp?topic=/com.vmware.vsphere.resourcemanagement.doc_41/performance_monitoring_utilities_resxtop_and_esxtop/r_memory_panel.html VMware shows the following values in esxtop: SWAP (MB) Displays the ESX/ESXi swap usage statistics. All numbers are in megabytes. curr Current swap usage. rclmtgt Where the ESX/ESXi system expects the reclaimed memory to be. Memory can be reclaimed by swapping or compression. r/s Rate at which memory is swapped in by the ESX/ESXi system from disk. w/s Rate at which memory is swapped to disk by the ESX/ESXi system. So, "r/s" shows memory being swapped in from disk. But I have tested and I have since freed up much RAM by migrating some of my guests to another host. I still see a considerable amount of memory swapped, though it is not growing. Will this memory only swap back to RAM once it is accessed?

What happens to memory that is swapped to disk after RAM is freed?

by Contributor in ESXi Discussions
‎03-19-2014 08:52 AM
‎03-19-2014 08:52 AM
I have a 2 host cluster. I want all VM's to run on one host in the event of a host failure. To test this, I vMotion all virtual machines to a single host while monitoring esxtop. I see that my VM... See more...
I have a 2 host cluster. I want all VM's to run on one host in the event of a host failure. To test this, I vMotion all virtual machines to a single host while monitoring esxtop. I see that my VMKMEM state goes from high, to soft, and quickly to hard, causing much memory to be swapped to disk. This is understandable, because page sharing and ballooning take some time to reclaim memory. After everything is settled down, I see that my host has 4GB of free memory, presumable reclaimed from page sharing, ballooning, and swapping. But, now that we have this much free memory, my RAM could now comfortably hold this data that was swapped. Is there such a thing as "unswapping" or swapping back to RAM? What happens to this 1GB that is swapped? Will it stay swapped until the guest frees it, possibly indefinitely hurting my memory performance, or will VMware move this memory back to RAM? When?

Re: Consumed Host Memory is higher than Guest usage(incl Cached) and overhead?

by Contributor in ESXi Discussions
‎03-19-2014 08:44 AM
‎03-19-2014 08:44 AM
I have confirmed with VMware that this is the reason the memory wasn't being reclaimed. They provided me the following link that has a nice low-level diagram showing how memory is managed and whe... See more...
I have confirmed with VMware that this is the reason the memory wasn't being reclaimed. They provided me the following link that has a nice low-level diagram showing how memory is managed and when: http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=2017642

Re: Consumed Host Memory is higher than Guest usage(incl Cached) and overhead?

by Contributor in ESXi Discussions
‎03-18-2014 09:03 AM
‎03-18-2014 09:03 AM
I think I found my answer in the "Understanding Memory Resource Management" guide here: http://www.vmware.com/files/pdf/mem_mgmt_perf_vsphere5.pdf Section "When to Reclaim Host Memory" page 15... See more...
I think I found my answer in the "Understanding Memory Resource Management" guide here: http://www.vmware.com/files/pdf/mem_mgmt_perf_vsphere5.pdf Section "When to Reclaim Host Memory" page 15: "In the high state, the aggregate virtual machine guest memory usage is smaller than the host memory size. Whether or not host memory is overcommitted, the hypervisor will not reclaim memory through ballooning or swapping. (This is true only when the virtual machine memory limit is not set.) If host free memory drops towards the soft threshold, the hypervisor starts to reclaim memory using ballooning. Ballooning happens before free memory actually reaches the soft threshold because it takes time for the balloon driver to allocate and pin guest physical memory. Usually, the balloon driver is able to reclaim memory in a timely fashion so that the host free memory stays above the soft threshold." I checked esxtop, pressing "m" for memory view, and I can see that the hosts VMKMEM shows "high state", so the only way memory is currently reclaimed is by page sharing. Only when I start to run out of host memory, this state changes to "soft" or "hard", will ballooning or swapping take place to free up the guest "free" memory. esxtop show my "minfree" as 940 MB, while it shows that I have 6960MB of free physically memory.

Re: Consumed Host Memory is higher than Guest usage(incl Cached) and overhead?

by Contributor in ESXi Discussions
‎03-18-2014 08:38 AM
‎03-18-2014 08:38 AM
This is an Active Directory Domain Controller, so also a database, but a relatively small one. What I don't understand, is that even in your example, if the guest OS shows 5.7GB of free memor... See more...
This is an Active Directory Domain Controller, so also a database, but a relatively small one. What I don't understand, is that even in your example, if the guest OS shows 5.7GB of free memory, that is memory that SQL is not using, it can't be using it if the guest hasn't allocated it. And if SQL is not using it, the guest is not using it, then why would the host be using it? Is this because the database is constantly cycling the "Free" memory" So this 5.7GB that was free 10 minutes ago is at a completely different memory location than the 5.7GB that is free right now, causing the host reclaimation of guest memory to not be able to keep up?

Re: Consumed Host Memory is higher than Guest usage(incl Cached) and overhead?

by Contributor in ESXi Discussions
‎03-18-2014 08:16 AM
‎03-18-2014 08:16 AM
I appreciate the extremely fast response, but I think it was made too hastily and without much detail. Yes I have looked through these documents. My understanding is that the balloon driver is us... See more...
I appreciate the extremely fast response, but I think it was made too hastily and without much detail. Yes I have looked through these documents. My understanding is that the balloon driver is used to swap some of the "least used" (but actually used) guest memory pages. This does not seem to apply here because this memory is actually "Free" on the guest, it should not need to be swapped. If the balloon driver also is there to allow a host to reclaim "Free" memory, then why is this memory not being reclaimed by the balloon driver if it has been consistently free for so long? The TPS feature also does not seem relevant here, because if anything, it would reduce the host memory usage, not explain why the host memory usage is actually so much higher.

Consumed Host Memory is higher than Guest usage(incl Cached) and overhead?

by Contributor in ESXi Discussions
‎03-18-2014 07:58 AM
‎03-18-2014 07:58 AM
I am running ESXi 5.1. I do not have any custom reservations configured for Memory. I am running in "Sandy Bridge" EVC mode. I notice higher than expected consumed host memory on many of my gu... See more...
I am running ESXi 5.1. I do not have any custom reservations configured for Memory. I am running in "Sandy Bridge" EVC mode. I notice higher than expected consumed host memory on many of my guests. This example guest is running Server 2012 R2 with current VMware tools version running. VMware reports Guest OS reports My understanding is that the "Standby" and "Modified" on the guest contains the "Cached" memory, and the guest "Cached" memory is the typical answer to this question that I see when people are onyl looking at the "In Use" memory. In my case, I am factoring in the cached memory, my guest shows 3805 MB of truely free memory, yet my host shows 7.68 GB of host memory consumed, with only 68MB of overhead consumption.By my calculations, the VM should only be consuming about 4.28GB of memory. Message was edited by: bradduane Replaced text values with screenshots.