Display memory information
memory
userview = memory
[userview,systemview] = memory
The memory function is available only on Microsoft®
Windows® systems. Results are dependent on your computer hardware and the
load on your computer.
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:
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:
[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:
Each of the sections below describes a value that is displayed or returned by the
memory function.
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.
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 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 |
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 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 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 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 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.
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: 784044032Assign 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+10MATLAB 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 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.
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.
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.