memory

Display memory information

Syntax

memory
userview = memory
[userview,systemview] = memory


Limitations

• The memory function is available only on Microsoft^® Windows^® systems. Results are dependent on your computer hardware and the load on your computer.

Description

memory displays information showing how much memory is available and how much the MATLAB^® software is currently using. The information displayed at your computer screen includes the following items, each of which is described in a section below:

• Maximum Possible Array

• Memory Available for All Arrays

• Memory Used By MATLAB

• Physical Memory (RAM)

userview = memory returns user-focused information on memory use in structure userview. The information returned in userview includes the following items, each of which is described in a section below:

• Maximum Possible Array

• Memory Available for All Arrays

• Memory Used By MATLAB

[userview,systemview] = memory returns both user- and system-focused information on memory use in structures userview and systemview, respectively. The userview structure is described in the command syntax above. The information returned in systemview includes the following items, each of which is described in a section below:

• Virtual Address Space

• System Memory

• Physical Memory (RAM)

Output Arguments

Each of the sections below describes a value that is displayed or returned by the memory function.

Maximum Possible Array

Maximum Possible Array is the size of the largest contiguous free memory block. As such, it is an upper bound on the largest single array MATLAB can create at this time.

MATLAB derives this number from the smaller of the following two values:

• The largest contiguous memory block found in the MATLAB virtual address space

• The total available system memory

To see how many array elements this number represents, divide by the number of bytes in the array class. For example, for a double array, divide by 8. The actual number of elements MATLAB can create is always fewer than this number.

When you enter the memory command without assigning its output, MATLAB displays this information in the Command Window. When you do assign the output, MATLAB returns the information in a structure field. See the table below.

Command	Returned in
memory	Character vector labeled Maximum possible array:
user = memory	Structure field user.MaxPossibleArrayBytes

All values are double-precision and in units of bytes.

Footnotes

When you enter the memory command without specifying any outputs, MATLAB may also display one of the following footnote on 64-bit systems:

Limited by System Memory (physical + swap file) available.

There is insufficient system memory to allow mapping of all virtual addresses in the largest available block of the MATLAB process.

Memory Available for All Arrays

Memory Available for All Arrays is the total amount of memory available to hold data. The amount of memory available is guaranteed to be at least as large as this field.

MATLAB derives this number from the smaller of the following two values:

• The total available MATLAB virtual address space

• The total available system memory

When you enter the memory command without assigning its output, MATLAB displays this information in the Command Window. When you do assign the output, MATLAB returns the information in a structure field. See the table below.

Command	Returned in
memory	Character vector labeled Memory available for all arrays:
user = memory	Structure field user.MemAvailableAllArrays

Footnotes

When you enter the memory command without specifying any outputs, MATLAB may also display the following footnote on 64-bit systems:

Limited by System Memory (physical + swap file) available.

There is insufficient system memory to allow mapping of all available virtual addresses in the MATLAB process.

Memory Used By MATLAB

Memory Used By MATLAB is the total amount of system memory reserved for the MATLAB process. It is the sum of the physical memory and potential swap file usage.

When you enter the memory command without assigning its output, MATLAB displays this information in the Command Window. When you do assign the output, MATLAB returns the information in a structure field. See the table below.

Command	Returned in
memory	Character vector labeled Memory used by MATLAB:
user = memory	Structure field user.MemUsedMATLAB

Physical Memory (RAM)

Physical Memory is the available and total amounts of physical memory (RAM) on the computer running MATLAB.

When you enter the memory command without assigning its output, MATLAB displays the total memory in the Command Window. When you do assign the output, MATLAB returns both the available and total memory in a structure field. See the table below.

Command	Value	Returned in
memory	Total memory	Character vector labeled Physical Memory (RAM):
[user,sys] = memory	Available memory	Structure field sys.PhysicalMemory.Available
	Total memory	Structure field sys.PhysicalMemory.Total

Available physical memory is the same as Available found in the Windows Task Manager: Performance/Physical Memory, and the total physical memory is the same as Total.

You can use the amount of available physical memory as a measure of how much data you can access quickly.

Virtual Address Space

Virtual Address Space is the amount of available and total virtual memory for the MATLAB process. MATLAB returns the information in two fields of the return structure: Available and Total.

Command	Return Value	Returned in Structure Field
[user,sys] = memory	Available memory	sys.VirtualAddressSpace.Available
	Total memory	sys.VirtualAddressSpace.Total

You can monitor the difference:

VirtualAddressSpace.Total - VirtualAddressSpace.Available

as the Virtual Bytes counter in the Windows Performance Monitor (e.g., Windows 7 Control Panel/Administrative Tools/Performance Monitor). If you add a counter, the Virtual Bytes counter is found under the Process menu. Select the counter, and then select MATLAB from the Instances of selected object pane.

System Memory

System Memory is the amount of available system memory on your computer system. This number includes the amount of available physical memory and the amount of available swap file space on the computer running MATLAB. MATLAB returns the information in the SystemMemory field of the return structure.

Command	Return Value	Returned in Structure Field
[user,sys] = memory	Available memory	sys.SystemMemory

This is the same as the difference:

limit - total (in bytes)

found in the Windows Task Manager: Performance/Commit Charge.

Examples

Display memory statistics on a 64-bit Windows system:

memory

Maximum possible array:            14253 MB (1.495e+10 bytes) *
Memory available for all arrays:            14253 MB (1.495e+10 bytes) *
Memory used by MATLAB:              747 MB (7.833e+08 bytes)
Physical Memory (RAM):            12279 MB (1.288e+10 bytes)

*  Limited by System Memory (physical + swap file) available.

Return in the structure userview, information on the largest array MATLAB can create at this time, how much memory is available to hold data, and the amount of memory currently being used by your MATLAB process:

userview = memory

userview = 

    MaxPossibleArrayBytes: 1.4957e+10
    MemAvailableAllArrays: 1.4957e+10
            MemUsedMATLAB: 784044032

Assign the output to two structures, user and sys, to obtain the information shown here:

[user,sys] = memory;

%  --- Largest array MATLAB can create ---
user.MaxPossibleArrayBytes

ans =
   1.4956e+10

%  --- Memory available for data ---
user.MemAvailableAllArrays

ans =
   1.4956e+10

%  --- Memory used by MATLAB process ---
user.MemUsedMATLAB

ans =
   784039936

%  --- Virtual memory for MATLAB process ---
sys.VirtualAddressSpace

ans = 
    Available: 8.7910e+12
        Total: 8.7961e+12

%  --- Physical memory and paging file ---
sys.SystemMemory

ans = 
    Available: 1.4956e+10

%   --- Computer's physical memory ---
sys.PhysicalMemory

ans = 
    Available: 2.7093e+09
        Total: 1.2876e+10

Tips

Details on Memory Used By MATLAB

MATLAB computes the value for Memory Used By MATLAB by walking the MATLAB process memory structures and summing all the sections that have physical storage allocated in memory or in the paging file on disk.

Using the Windows Task Manager, you have for the MATLAB.exe image:

Mem Usage < MemUsedMATLAB < Mem Usage + VM Size (in bytes)

where both of the following are true:

• Mem Usage is the working set size in kilobytes.

• VM Size is the page file usage, or private bytes, in kilobytes.

The working set size is the portion of the MATLAB virtual address space that is currently resident in RAM and can be referenced without a memory page fault. The page file usage gives the portion of the MATLAB virtual address space that requires a backup that doesn't already exist. Another name for page file usage is private bytes. It includes all MATLAB variables and workspaces. Since some of the pages in the page file may also be part of the working set, this sum is an overestimate of MemUseMATLAB. Note that there are virtual pages in the MATLAB process space that already have a backup. For example, code loaded from EXEs and DLLs and memory-mapped files. If any part of those files is in memory when the memory builtin is called, that memory will be counted as part of MemUsedMATLAB.

Reserved Addresses

Reserved addresses are addresses sets aside in the process virtual address space for some specific future use. These reserved addresses reduce the size of MemAvailableAllArrays and can reduce the size of the current or future value of MaxPossibleArrayBytes.

Example 1 — Java Virtual Machine (JVM)

At MATLAB startup, part of the MATLAB virtual address space is reserved by the Java^® Virtual Machine (JVM™) and cannot be used for storing MATLAB arrays.

Example 2 — Standard Windows Heap Manager

MATLAB, by default, uses the standard Windows heap manager except for a set of small preselected allocation sizes. One characteristic of this heap manager is that its behavior depends upon whether the requested allocation is less than or greater than the fixed number of 524,280 bytes. For, example, if you create a sequence of MATLAB arrays, each less than 524,280 bytes, and then clear them all, the MemUsedMATLAB value before and after shows little change, and the MemAvailableAllArrays value is now smaller by the total space allocated.

The result is that, instead of globally freeing the extra memory, the memory becomes reserved. It can only be reused for arrays less than 524,280 bytes. You cannot reclaim this memory for a larger array except by restarting MATLAB.