Move physical memory usage to virtual memory -- unveiling

Source: Internet
Author: User

See VB (or any program) to move physical memory usage to virtual memory

So why can my program move the occupied memory to the virtual memory?

In fact, you can also try to minimize a program to the taskbar, and then look at the task manager. No, the actual memory occupied by your program is suddenly reduced, it seems that I don't have any way to compress the memory, but the operating system itself has this mechanism, that is, when the program is not in use (minimized), the operating system will call some commands, to move the memory occupied by the program to the virtual memory and retain only a small portion of the common code.

So we can see that the memory usage is reduced at once.

So: what commands did the system call? Can I release the memory without narrowing down the form?

Look at this APISetprocessworkingsetsize

This is the original answer from msdn.

UsingSetprocessworkingsetsizeFunction to set an application's minimum and maximum working set sizes does not guarantee that the requested memory will be reserved, or that it will remain resident at all times. when the application is idle, or a low-memory situation causes a demand for memory, the operating system can reduce the application's working set. an application can useVirtuallockFunction to lock ranges of the application's virtual address space in memory; however, that can potentially degrade the performance of the system.

Use this function to set the minimum and maximum runtime space of the application, and only reserve the required memory. When the application is idle or the system memory is too low, the operating system will automatically call this mechanism to set the application memory. Applications can also useVirtuallockTo lock a certain range of memory from being released by the system.

When you increase the working set size of an application, you are taking away physical memory from the rest of the system. this can degrade the performance of other applications and the system as a whole. it can also lead to failures of operations that require physical memory to be present; for example, creating processes, threads, and kernel pool. thus, you must useSetprocessworkingsetsizeFunction carefully. You must always consider the performance of the whole system when you are designing an application.

When you increase the runtime space for applications, the physical memory you can obtain depends on the system, which may cause other applications to degrade performance or the overall system performance, this may also cause the request to the physical memory operation to fail. For example, to create a process, thread, or kernel pool, you must use this function with caution.


In fact, using this function does not improve performance or actually save memory.

Because it only temporarily moves the memory occupied by the application to the virtual memory. Once the application is activated or has an operation request, the memory will be occupied again. If you use this method to set the memory occupied by the program, the system performance may be reduced to some extent because the system needs to frequently perform page exchanges between the memory and the hard disk.

Bool Setprocessworkingsetsize (
Handle Hprocess,
Size_t Dwminimumworkingsetsize,
Size_t Dwmaximumworkingsetsize

Set the two size_t parameters to-1, that is, the memory used by the process can be switched to the virtual memory, only a small part of the code is retained.

The reason why the table calendar show can always keep the Minimum Memory is that the timer is used and the operation is not stopped. Therefore, the performance can be imagined. Although it is in exchange for the illusion of small memory, it is indeed a disaster for the system.

Of course, this function is not all right,

1. When our application is just loaded, you can use this operation once to put the code not required in the loading process into the virtual memory. In this way, after the program is loaded, maintain a large amount of available memory. VB

2. When the program runs for a certain period of time or the program is about to be idle, you can use this command to swap the occupied memory to the virtual memory.

Finally, attach the API code called by VB

Option explicit
Private declare function setprocessworkingsetsize lib "Kernel32" (byval hprocess as long, byval dwminimumworkingsetsize as long, byval dwmaximumworkingsetsize as long) as long
Private declare function getcurrentprocess lib "Kernel32" () as long

Setprocessworkingsetsize getcurrentprocess,-1,-1

Place the memory used by the current process to 0.

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