vSphere Memory Managment

[SunilSaini]

Hi All

I have the confusion of working of the Terms like -- pmap, shadow page table, and TLB.

How these component are works. when these address space gets update and by which component.

Its very confusing for me

Thanks in advance..

[bkarthikkeyan]

hi to be clear please read the doc released by vmware i have also attached the same document .

regards

Karthikeyan

[idle-jam]

this is another good read for your understanding: http://www.vmware.com/pdf/vsphere4/r40/vsp_40_resource_mgmt.pdf

[SunilSaini]

Thanks a lot of you both.

I also had gone through these Doc and got confused.

On the page no. 4 "in ESX, the address translation between guest physical memory and host physical memory is maintained
by the hypervisor using a physical memory mapping data structure, or pmap, for each virtual machine. The hypervisor intercepts
all virtual machine instructions that manipulate the hardware translation lookaside buffer (TLB) contents or guest operating system
page tables, which contain the virtual to physical address mapping. The actual hardware TLB state is updated based on the separate
shadow page tables, which contain the guest virtual to host physical address mapping. The shadow page tables maintain consistency
with the guest virtual to guest physical address mapping in the guest page tables and the guest physical to host physical address"

Above statement is from the doc suggested by you. There is no defination for the TLB (what does TLB, whats the use of TLB here ) and shadow page table which keep the consistancy between guest virtual, guest physical and host physical maping table. And there is no explaination how the shadow page table gets update about the gust virtual to guest physical tables. Becouse hypersior does not keep the information about guest OS in virtual machine. Hypersion is not aware about the idle memory which is not used by the guest OS.

I hope your quick responce.

Thanks in Advance

[idle-jam]

look at page 31 on memory reclamation and how idle memory is being assigned for busier VM.

[SunilSaini]

I am very thankful to you for your quick response.

My question is not about the memory reclamation. Memory reclamation comes in role when host is overcommitted. My question is about the memory distribution. How the hypervisor comes to know about the guest OS page table (Guest virtual memory mapping to Guest physical memory mapping). If it is true that hypervisor has no idea about the Guest OS.

Thanks a lot.