Who Owns Virtual Memory?

Given a virtual address, the procedure for determining who owns and is using this memory essentially amounts to the following steps:

• If the question of ownership relates to a known process's private storage then determine its hptda.

• Locate the arena record(s) that encompass the address.

• If more than one then select the one that relates to the process of interest (if known) by matching the hptda.

• Locate the object records that are chained to the arena record.

• If more than one then select the process of interest by matching the hptda.

• Note the own and hmte values and their interpretation on the right-hand side of the VMOB display.

• If necessary format the own and hmte VMOBs.

• If either is an MTE then use .LM or .LMO, with the hob as parameter, to format the MTE.

• If the memory is shared (hco=nnnnn appears in the arena record display) then format the chain of VMCOs and select the one that matches hptda from step 1.

Fortunately this task is reduced in complexity because of the M or match option that exists with both the .MO and .MA commands.

.MOM addr will display the VMOB of a pseudo-object that matches the addr if it exists. PTDAs are pseudo-objects and their addresses are listed by the .P command.

.MAM addr will search for all arena records whose address range encompasses addr. Under the kernel Debugger this search is restricted to the current context unless the A option (all contexts) is also specified. Under the dump formatter A in always in effect.

The C option further reduces the effort. This is the chain option and is applicable to .MO, .MA, .MC and .ML commands. Chaining formats all VMOBs, VMARs, VMCO and VMALs that are chained from each VMAR associated with the VM control block being formatted.

.MAMC (or .MAMAC under the DF) are the default options if just .M is specified. Furthermore the matching address defaults to the current CS:EIP.

The following sections illustrate memory ownership in:

Shared Arena Global Data

Shared Arena Instance Data

Private Arena Shared and Private Data

Physical Storage.

Further examples in memory management exploration, including looking at aliasing may be found in Exploring Memory Management.