Transparent Page Sharing (TPS) in vSphere 6.0 PART3

Also do check Ballooning. Compression articles in this series on VMware Memory Reclamation.
On ESXi host, you may have several virtual machines that are running with same guest operating system, have the same applications, or contain the same user data. Due to this, there is possibility that memory pages created by virtual machines are similar in terms of content. So instead of creating similar multiple pages in host memory for each virtual machine, TPS is used to perform memory page sharing.

In vSphere 6, intra-VM TPS is enabled by default and inter-VM TPS is disabled by default, due to some security concerns as described in VMware KB 2080735.

With page sharing, the hypervisor reclaims the redundant copies and keeps only one copy, which is shared by multiple virtual machines in the host physical memory. As a result, the total virtual machine host memory consumption is reduced and a high memory over commitment is possible.

How TPS works? 

ESXi scans the content of guest physical memory for sharing opportunities. Instead of comparing each byte of a candidate guest physical page to other pages, ESXi uses hashing to identify potentially identical pages. 

Image: VMware

• A hash value is generated based on the virtual machines physical page’s (GA) content and stored in global hash table. Each entry in global hash table includes a hash value and the physical page number of a shared page
• The hash value is used to look up a global hash table. If the hash value of virtual machines physical page matches an existing entry in hash table, a bit-by-bit comparison of the page contents is performed to exclude any false match. 
• Once the virtual machine physical page’s content matches with the content of an existing shared host physical page, the guest physical (GA) to host physical mapping (HA) of the virtual machine physical page is changed to the shared host physical page, and the redundant host memory copy (the page pointed to by the dashed arrow in above image) is reclaimed. 
• This remapping is invisible to the virtual machine and inaccessible to the guest operating system. Because of this invisibility, sensitive information cannot be leaked from one virtual machine to another.

Image:VMware

• Any attempt to write to the shared pages will generate a minor page fault. In the page fault handler, the hypervisor will transparently create a private copy of the page for the virtual machine and remap the affected guest physical page to this private copy. A standard copy-on-write (CoW) technique is used to handle writes to the shared host physical pages. 

In hardware-assisted memory virtualization (Intel EPT and AMD RVI) systems, ESXi will not share large pages because: 

• The probability of finding two large pages having identical contents is low

• The overhead of doing a bit-by-bit comparison for a 2MB page is much larger than for a 4KB page

Since ESXi will not swap out large pages, the large page (2MB) will be broken into small pages (4KB) during host swapping so that these pre-generated hashes can be used to share the small pages before they are swapped out. 

What is Salting in TPS?


Salting is used to allow more granular management of the virtual machines participating in TPS. Salting is enabled after the ESXi update mentioned below are deployed.

• ESXi 5.0 Patch ESXi500-201502001
• ESXi 5.1 Update 3
• ESXi 5.5, Patch ESXi550-201501001
• ESXi 6.0

By default, salting is set Mem.ShareForceSalting=2 and each virtual machine has a different salt. This means page sharing does not occur across the virtual machines (inter-VM TPS) and only happens inside a virtual machine (intra VM).

When salting is enabled (Mem.ShareForceSalting=1 or 2) in order to share a page between two virtual machines both salt and the content of the page must be same. A salt value is a configurable vmx option for each virtual machine. You can manually specify the salt values in the virtual machine's vmx file with the new vmx option sched.mem.pshare.salt. If this option is not present in the virtual machine's vmx file, then the value of vc.uuid vmx option is taken as the default value. Since the vc.uuid is unique to each virtual machine, by default TPS happens only among the pages belonging to a particular virtual machine (Intra-VM).

How can I enable or disable salting?

1. Log in to ESX (i)/vCenter with the VI-Client. 
2. Select ESX (i) relevant host. 
3. In the Configuration tab, click Advanced Settings (link) under the software section. 
4. In the Advanced Settings window, click Mem.  
5. Search for Mem.ShareForceSalting and set the value to 1 or 2 (enable salting), 0(disable salting). 
6. Click OK. 
7. For the changes to take effect do either of the two: 
   • Migrate all the virtual machines to another host in cluster and then back to original host. Or 
   • Shutdown and power-on the virtual machines.

Steps to specify the salt value for a virtual machine:

1. Power off the virtual machine on which you want to set salt value.   
2. Right click on virtual machine, click on Edit settings.   
3. Select options menu, click on General under Advanced section. 
4. Click on Configuration Parameters…. 
5. Click on Add Row, new row will be added. 
6. On LHS add text sched.mem.pshare.salt and on RHS specify the unique string. 
7. Power on the virtual machine to take effect of salting. 
8. Repeat steps 1 to 7 to set the salt value for individuals virtual machine. 

Note: Same salting values can be specified to achieve the page sharing across virtual machines.
  
You can change the TPS behavior by applying the salting mechanism as described in VMware KB 2097593.

Below is the list of articles in this series for further reading.

PART1: Run cycle of reclamation techniques
PART2: Mem.minfreepct and sliding scale method 

PART4: VMware Ballooning 
PART5: VMware Memory Compression
PART6: Hypervisor Swapping and Host SSD Swap

Horizon 7 Demo - Admin UI - Security Protection Layer

Horizon 7 Instant Clone Pool Creation Demo

Horizon 7 Instant Clones Deep Dive

Horizon 7 Blast Extreme Deep Dive

Horizon 7 Platform Deep Dive

Horizon Client and Agent Deep Dive

Cloud Pod Architecture feature in Horizon 7

Part I

Part II:

Part III:

 

VMware NSX for Horizon

Horizon View 6.X Desktop Pool types.

In Horizon View 6.X there are 3 types of Desktop pools that we can create as per the requirements. These 3 types are as listed below.

• Manual Desktop Pool
• Automated Desktop Pool
• RDSH Desktop Pool

Manual Pool:

This type of pool can contain managed VMs (Existing VMs that are managed by vCenter Server), unmanaged systems (VMs managed by VMware Server, Physical Computers, Blade PCs).

As the name suggest, desktops are not provisioned automatically. At the time of creation of pool, you need to select systems that are going to be member of this pool.

Automated Pool:

In this type of pool, member desktops are automatically created by Connection server using two different methods.

One method is to  use virtual machine templates to create new desktops. These VMs are also called as full clones alternatively.

Another method is called as linked clone technology. Will write about linked clones separately as this is vast topic.

RDSH Pool:

In this type of pool, RDS sessions are provided as machines to View users. Microsoft RDS host can be installed in virtual machine or Physical server. Connection server manages the sessions much like normal  machines.

VMware Horizon 6.x suite editions

VMware Horizon suite contains multiple products inside it like Horizon View, VMware Mirage, VMware Workspace and new addition like VMware Identity manager.  Below is the information about each edition that is available with Horizon 6.X suite  along with its components and features along with license models.

Standard Edition:

This version includes a standalone version of View, VMware ThinApp, vSphere Desktop, and vCenter Desktop. Horizon Standard Edition and its components are licensed per concurrent connection.

Per concurrent connection license model is for virtual environments with a high number of users who share machines throughout the day such as students and shift workers.

Advanced Edition:

In addition to the features in Horizon Standard Edition, this edition also includes the functionality for hosted applications, a unified workspace with VMware Workspace Portal, virtual storage with VMware Virtual SANTM, and image management for physical desktops using VMware Mirage and VMware Fusion® Pro.

License entitlement for Horizon 6 Advanced Edition is available as concurrent user and named user. Per named user license model is for virtual environments with staff that need dedicated access to a virtual machine throughout the day.

(VMware Identity Manager is replacing Workspace Portal in the Horizon 6 Advanced and Enterprise editions.)

Enterprise Edition:

This edition includes all features of Horizon View Standard Edition and Horizon Advanced Edition, also Horizon Enterprise Edition includes VMware vRealize Operations Manager for Horizon.

Horizon Enterprise Edition also includes the VMware vRealize Orchestrator plug-in that enables automated provisioning of desktops and applications using vRealize Orchestrator and vRealize Automation.

License entitlement for Horizon Enterprise Edition is available as concurrent user and named user.

vSphere Desktop included in Horizon editions has the same features and functionality of VMware vSphere Enterprise Plus Edition. This also means that if you already have VMware vSphere Enterprise Plus Edition, you can use this license with Horizon suite.

 Horizon 7 Suite is also in news and you can find more details about the it at VMware Portal.