JP2002328811A - Virtual storage method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize partial virtual storage on an operating system to be operated in a direct mode. SOLUTION: A task memory switching means 111 of a task dispatcher 101 switches task memories in the case of switching tasks, a task terminating means 112 releases a block of secondary storage corresponding to the task memory of the task to be terminated, a task memory securing means 113 of memory pool management 102 allocates the block of the secondary storage to the task memory by using a secondary storage block securing means 115 of a use state management 103 of secondary storage block when the memory is secured from a memory pool applicable to the task memory and a task memory releasing means 114 releases the block of the secondary storage allocated to the task memory by using a secondary storage block releasing means 116 when the memory pool applicable to the task memory is opened.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a virtual storage method, and more particularly, to a virtual storage method for providing a partial virtual storage to an operating system (having no virtual storage) operating in a direct mode.

[0002]

2. Description of the Related Art Conventionally, in embedded devices, the mounting memory capacity is severely limited due to restrictions on the size and cost of the device. Usually, an embedded real-time operating system emphasizes performance and operates in a direct mode without a virtual memory.

[0003]

However, in recent years,
While embedding devices place emphasis on performance, programs such as mobile terminals can download programs, and the need to coexist with the execution environment of application programs that perform large-capacity data processing has arisen. . However, in the conventional case, since the real-time operating system for embedded devices operates in the direct mode without virtual memory, it is impossible for an application program to use a memory larger than the mounted memory capacity. However, there is a problem that it is not possible to execute an application program for performing the above data processing.

[0004] The present invention has been made in view of such a situation, and enables an application program to use a memory larger than a mounted memory capacity on an operating system operating in a direct mode, thereby providing a large-capacity memory. An application program for performing data processing can be executed.

[0005]

According to a first aspect of the present invention, there is provided an information processing apparatus comprising a memory and a secondary storage, wherein execution of a plurality of tasks is controlled by an operating system operating in a direct mode. A virtual storage method, comprising: a mapping step of mapping at least a part of a memory to a secondary storage for each task; and, when switching a task, the contents of the memory used by the task before the switching correspond to the memory. It is characterized by comprising a saving step of saving to the mapping destination of the secondary storage and a recovery step of restoring the contents of the memory used by the task after switching from the mapping destination of the secondary storage corresponding to the memory. Further, a part of the memory and the secondary storage can be respectively divided into blocks of a predetermined size, and managed by the block numbers assigned to the respective blocks. Further, based on a memory mapping table indicating a correspondence relationship between each block of a part of the memory and the block of the secondary storage to which each block is mapped, saving and restoring of the memory at the time of task switching are performed in block units. Can be In addition, the task memory virtually provided for each task is divided into blocks of a predetermined size, managed by block numbers assigned to each block, and each block of the task memory and each block are assigned to each task. Based on the task memory mapping table indicating the correspondence relationship with the blocks of the secondary storage mapped to the memory, the contents of the memory mapping table are rewritten with the contents of the task mapping table of the switched task at the time of task switching. be able to. In addition, based on a use status table indicating the use status of each block of the secondary storage, when there is free space in the secondary storage, the task memory can be mapped to the secondary storage. The information processing device according to claim 6,
An information processing apparatus comprising a memory and a secondary storage, wherein execution of a plurality of tasks is controlled by an operating system operating in a direct mode, wherein at least a part of the memory is mapped to a secondary storage for each task. Means for saving the contents of the memory used by the task before switching to the secondary storage mapping destination corresponding to the memory at the time of the task switching; and storing the contents of the memory used by the task after the switching. Recovery means for recovering from the secondary storage mapping destination corresponding to the memory. A virtual storage control program according to claim 7, wherein the virtual storage control program includes a memory and a secondary storage, and controls an information processing apparatus in which execution of a plurality of tasks is controlled by an operating system operating in a direct mode. Mapping at least a portion of the memory to the secondary storage for each task; and when switching the tasks, the contents of the memory used by the task before the switching are mapped to the secondary storage corresponding to the memory. And causing the information processing apparatus to execute a step of saving the contents of the memory used by the task after the switching from a mapping destination of the secondary storage corresponding to the memory. In the virtual storage method according to the present invention, at least a part of the memory is mapped to the secondary storage for each task, and at the time of task switching, the contents of the memory used by the task before switching correspond to the memory. The contents are saved to the secondary storage mapping destination, and the contents of the memory used by the task after switching are restored from the secondary storage mapping destination corresponding to the memory.

[0006]

FIG. 1 is a block diagram showing a configuration example of an embodiment of an operating system of an embedded device to which the present invention is applied. As shown in the figure, in the present embodiment, a task dispatcher 101 that performs task switching, a memory pool management 102 that performs memory pool management, and a secondary storage block usage management 103 that performs secondary storage block usage management It is composed of
Here, the memory pool is a real memory, and is allocated to a task memory (virtual memory) described later.

[0007] When the task dispatcher 101 switches tasks, the task dispatcher 101 switches a task memory (an area on a memory used as a virtual memory whose address is determined in advance) to a task memory switching unit 111 for switching the task to be dispatched next. And a task memory ending means 112 for releasing a block of the secondary storage used for the task memory held by the task when the task ends.

[0008] The memory pool management 102, when reserving memory from the memory pool corresponding to the task memory,
A task memory securing unit 113 for allocating a secondary storage block to the task memory; and a task memory release for releasing the secondary storage block allocated to the task memory when releasing the memory to the memory pool corresponding to the task memory. And means 114.

[0009] The secondary storage block usage status management 103 includes:
It comprises a secondary storage block securing means 115 for managing the use status of the blocks of the secondary storage, and a secondary storage block releasing means 116.

It is assumed that the operating system that controls each section of the present embodiment operates in the direct mode, and that its memory management is based on the memory pool method often found in embedded systems (for example, μITRO).
N (Industrial TRON (The Real
time Operating system Nuc
leus)) etc.). That is, the memory (RAM (land)
om access memory)) is managed by being divided into several continuous areas of addresses called memory pools, and a user (an application program (hereinafter, appropriately referred to as an application)) secures a memory from which area. Is specified by the ID of the memory pool. In the present embodiment, an area at a predetermined address in a memory is set as a memory pool unique to each task, and this area is saved and restored in a secondary storage (for example, a flash memory) at the time of a task switch. This allows an application to use a memory larger than the mounted memory capacity. This application may be composed of multiple tasks.

As shown in FIG. 2, the storage area of the secondary storage is divided into blocks of a predetermined input / output size (a size that can be read / written by one input / output), which is an input / output unit of the secondary storage. The blocks are managed by a block ID that uniquely indicates each block. It is assumed that input and output to and from the secondary storage can be performed directly by designating the block ID. Hereinafter, the size of each block is referred to as a block size.

In order to manage the use status ("in use" or "free") of each block of the secondary storage, a secondary storage use status table (each block of the secondary storage) as shown in FIG. Table showing the usage status of). FIG.
Shows an example of a secondary storage usage table. FIG.
In the example shown in FIG. 7, for example, it is indicated that the block number # 1 is “in use” and the block number # 3 is “empty”.

As shown in FIG. 4, a real memory used as a task memory (virtual storage) whose address is determined in advance has a secondary storage block size corresponding to a secondary storage block to be saved and restored. The blocks are divided into the same size, each block is assigned a block number, and managed by the block number.

FIG. 5 shows an example of a block mapping table which indicates in which block of the secondary memory each block of the real memory is saved. In this example, the block with the block number # 1 in the real memory corresponds to the block with the block number # 12 in the secondary memory, and the block with the block number # 2 in the real memory has the block number # 39 in the secondary storage. The block having the block number # 3 in the real memory corresponds to the block having the block number # 22 in the secondary memory, and the block having the block number # 4 in the real memory corresponds to the block having the block number # 8 in the secondary memory. The block with the block number N in the real memory corresponds to the block with the block number X in the secondary memory.

In the entire system, as shown in FIG. 6, one secondary storage use state table 605 for managing the use state of the secondary storage, and each block of the real memory in the task memory area, One block mapping table 601 for managing the real memory state indicating which block information is stored, and for managing which block of the secondary memory each block of the task memory in each task is saved to The block mapping tables 602 to 604 provided for each task are used.

The secondary storage usage table 605 indicates that all blocks are “empty” when the operating system is started.
Initialized as In the block mapping table 601 of the real memory, all blocks are initialized to “0” when the operating system is started. Also,
Block mapping tables 602 to 60 for each task
4 is created when each task is generated, and all blocks are initialized as “0”.

Next, the overall operation of the present embodiment will be described in detail with reference to the flowcharts of FIGS.

First, referring to the flowchart of FIG.
The task memory switching process will be described. When the task of the operating system is switched, in the task dispatcher 101 of FIG. 1, the task memory switching unit 111 switches the task memory to that of the task to be dispatched next. In the following, as shown in FIG. 6, from the state where the current task is “task 1”,
The operation of the task memory switching unit 111 when switching to the state where the current task is “task 2” will be described with reference to the flowchart in FIG.

First, a block mapping table 602 for task 1 is obtained (step 701). Next, the blocks registered in the block mapping table 602 are saved in the secondary storage in the following procedure. First, in step 702, steps 703 and 7 are executed for all entries of the block mapping table 602 of task 1.
Control is performed such that the process of step 04 is repeatedly executed. That is, it is determined whether or not the processing of steps 703 and 704 has been executed for all entries of the block mapping table 602 of task 1. As a result, if it is determined that the processing of steps 703 and 704 has not been executed for all entries of the block mapping table 602 of task 1, the process proceeds to step 703.

In step 703, for each entry of the block mapping table 602 for task 1 (each block of the real memory in the task memory area of task 1), the block number of the corresponding secondary storage block is not 0 in order. It is determined whether or not. As a result, when it is determined that the block number of the corresponding block of the secondary storage is 0, the process returns to step 702, and the processes after step 702 are repeatedly executed. On the other hand, when it is determined that the block number of the corresponding block of the secondary storage is not 0,
The data of the above block of the real memory in the task memory area is written into the block of the corresponding secondary storage block number by WR.
ITE is performed (step 704).

The block mapping table 602 shown in FIG.
In the example, the block numbers of the secondary storage corresponding to the blocks 1 to 3 of the real memory are not 0, so that the memory contents of the blocks 1 to 3 of the real memory are respectively stored in the block numbers # 3 and # 5 of the secondary storage. , # 8. That is, the memory contents of the block 1 of the real memory are WRITE to the block of the block number # 3 of the secondary memory, and the memory contents of the block 2 of the real memory are WRITE to the block of the block number # 5 of the secondary memory. Is written to the block of block number # 8 in the secondary storage.

In step 702, task 1
If it is determined that the processing of steps 703 and 704 has been performed for all entries of the block mapping table 602, the processing proceeds to step 705.

Next, the memory contents of task 2 to be dispatched after task 1 are recovered. First, a block mapping table 603 for task 2 is obtained (step 70).
5). Next, the blocks registered in the block mapping table 603 are recovered from the secondary storage in the following procedure. First, in step 706, control is performed so that the processing in step 707 and subsequent steps is repeatedly executed for all entries of the block mapping table of task 2. That is, it is determined whether or not the processing after step 707 has been executed for all entries of the block mapping table of task 2. As a result, if it is determined that the processing after step 707 has not been executed for all entries of the block mapping table of task 1, the process proceeds to step 707.

In step 707, for each entry of the block mapping table of task 1 (each block of the real memory in the task memory area of task 2), it is determined whether the block number of the corresponding secondary storage block is not 0. Is determined. As a result, when it is determined that the block number of the corresponding block of the secondary storage is 0, the process returns to step 706, and the processes after step 706 are repeatedly executed. On the other hand, when it is determined that the block number of the corresponding block of the secondary storage is not 0, the process proceeds to step 708.

In step 708, the block number of the secondary storage block corresponding to each block of the block mapping table 603 of task 2 and the block number of the secondary storage block corresponding to each block of the real memory block mapping table 601 are set. Whether or not the block numbers are equal is determined for each block in the block mapping table 603 of task 2 in order. As a result, the block number of the secondary storage block corresponding to each block of the block mapping table 603 of task 2 is equal to the block number of the secondary storage block corresponding to each block of the block mapping table 601 of the real memory. If it is determined that there is no
The processes after 06 are repeatedly executed.

On the other hand, the block number of the secondary storage block corresponding to each block of the block mapping table 603 of the task 2, the block number of the secondary storage block corresponding to each block of the block mapping table 601 of the real memory, and the like. Is determined to be not equal (different), the data of the block of the block number of the corresponding secondary storage in the block mapping table 603 of task 2 is read and written to the corresponding block of the real memory (step 709). At this time, the block number of the corresponding secondary storage in the block mapping table 601 of the real memory is updated to the block number of the read block (step 710). Then, returning to step 706,
The processing after step 706 is repeatedly executed. In step 706, step 7 is executed for all entries of the block mapping table 603 of task 2.
When it is determined that the processes of 07 to 710 have been executed,
This processing ends.

In the example of the block mapping table 603 shown in FIG.
The block number of the secondary storage corresponding to the items 3 to 3 is not 0,
The block numbers of the secondary storage corresponding to the blocks 1 to 3 of the task 2 and the block numbers of the secondary storage corresponding to the blocks 1 to 3 of the block mapping table 601 of the real memory are different from each other (task 2). The block number of the secondary storage corresponding to the block 1 of the task memory is # 1, and the block number of the secondary storage corresponding to the block 1 of the real memory is # 3. The corresponding secondary storage block number is # 2, and the secondary storage block number corresponding to the real memory block 2 is # 5, and the secondary storage block corresponding to the task memory block 3 of task 2. The number is # 6, and the block number of the secondary storage corresponding to the block 3 of the real memory is different at # 8). It is the block number # 1 of the secondary storage, #
READ from the blocks # 2 and # 6, and rewrite the blocks 1 to 3 of the block mapping table 601 of the real memory to the contents of the blocks corresponding to the currently read block numbers # 1, # 2 and # 6. Since the block number of the secondary storage corresponding to the block 4 of the task memory of the task 2 and the block number of the secondary storage corresponding to the block 4 of the real memory are both equal to # 9, the block 4 is left as it is. .

Next, the processing procedure at the end of a task will be described. At the end of the task, the terminator of the task of the operating system is the task memory ending means 1
12 (FIG. 1), the task memory of the task is released. Hereinafter, with reference to the flowchart of FIG.
Will be described as an example.

First, a block mapping table 602 for task 1 is obtained (step 801). Next, the blocks registered in the block mapping table 602 are released in the following procedure. First, in step 802, control is performed such that the processing of steps 803 and 804 is repeatedly executed for all entries of the block mapping table 602 of task 1. That is, task 1
It is determined whether or not the processing of steps 803 and 804 has been executed for all the entries of the block mapping table 602 of FIG. As a result, for all entries of the block mapping table 601 of task 1, step 8
If it is determined that the processing of 03,804 has not been executed, the process proceeds to step 803.

In step 803, for each entry of the block mapping table 601 of task 1 (each block of the real memory in the task memory area of task 1), whether the block number of the corresponding secondary storage block is not 0 is determined. It is determined whether or not. As a result, when it is determined that the block number of the corresponding block of the secondary storage is 0, the process returns to step 802, and the processes after step 802 are repeatedly executed. On the other hand, when it is determined that the block number of the corresponding block of the secondary storage is not 0,
The secondary storage block releasing means 116 (FIG. 1) releases the block of the secondary storage block number (step 8).
04).

In step 802, task 1
If it is determined that the processing of steps 803 and 804 has been executed for all the entries of the block mapping table 601 of FIG.

In the example of the block mapping table 602 shown in FIG. 6, since the block numbers of the secondary storage corresponding to the blocks 1 to 3 are not 0, the block numbers # 3, # 5, # 8 corresponding to these blocks are used. Free the block of secondary storage of.

Next, a processing procedure for securing a memory will be described. When a task secures memory from the memory pool, the operating system memory pool management 10
2 (FIG. 1) indicates that when the specified memory pool is a task memory, that is, when the specified memory pool is a part of a memory pool to which secondary storage is mapped according to the task memories of a plurality of tasks, The included block is secured by using the task memory securing means 113 (FIG. 1). Hereinafter, the operation of the task memory securing unit 113 will be described with reference to the flowchart of FIG. 9 by taking as an example the case where “task 1” secures the memory.

First, the block number of the corresponding memory is obtained from the address and size of the memory to be secured (depending on the method of managing the free space in the memory pool of the operating system, a pointer for managing the free area is stored in the free memory. In this case, all the memories to be used, including the area for storing the pointer, need to be “secured.” However, the operating system according to the present embodiment has It is assumed that the operating system does not perform any management, and only needs to pay attention to the reserved memory.)
Depending on the position and size of the block, the block may span a plurality of blocks. In this case, a plurality of block numbers are obtained (step 901).

Next, a block mapping table 602 for task 1 is obtained (step 902). Next, for each block number obtained in step 901, step 904
906 are controlled so as to be executed (step 903). That is, it is determined whether or not the processing of steps 904 to 906 has been performed for all the block numbers obtained in step 901. As a result, if it is determined that the processing of steps 904 to 906 has not been executed for all block numbers, step 904
Proceed to.

In step 904, it is determined whether the block number of the secondary storage is 0 in the block mapping table 602 of the task 1. as a result,
When it is determined that the block number of the secondary storage corresponding to the block mapping table 602 of the task 1 is not 0, the process returns to the step 903, and the processes after the step 903 are repeatedly executed. On the other hand, when it is determined that the block number of the secondary storage corresponding to the block mapping table 602 of the task 1 is 0, the process proceeds to step 905.

In step 905, the secondary storage block securing means 115 (FIG. 1) secures a block of a predetermined block number in the secondary storage, and assigns the block number to the block mapping table 602 of the task 1. (To be entered in the entry of the block mapping table 602). Also,
The block number is also stored as the corresponding secondary storage block number in the block mapping table 601 of the real memory (entry is also entered in the entry of the block mapping table 601) (step 906). Thereafter, the process returns to step 903, and the processing after step 903 is repeatedly executed.

Further, in step 903, steps 904 to 906 are performed for all block numbers of the real memory.
If it is determined that the process has been executed, the present process is terminated.

Next, a processing procedure for releasing the memory will be described. When the task releases the memory to the memory pool, the memory pool management 102 of the operating system (FIG. 1) allocates the block containing the released memory to the task memory releasing unit 114 (FIG. 1) when the designated memory pool is the task memory. Release with. Less than,
With reference to the flowchart of FIG. 10, the operation of the task memory release unit 114 will be described by taking as an example the case where “task 1” releases the memory.

First, as a result of releasing the memory, the block number of the unused memory is obtained. Depending on the release position and size, a plurality of blocks may be unused. In this case, a plurality of block numbers are obtained (step 100).
1). Next, block mapping table 6 of task 1
02 (step 1002). Next, step 10
Control is performed so that the processing of steps 1004 and 1005 is executed for all the block numbers obtained in 01 (step 1003).

Next, in step 1004, it is determined whether or not the block number of the corresponding secondary storage in the block mapping table 602 is not 0. As a result, when it is determined in the block mapping table 602 that the block number of the corresponding secondary storage is 0, the process returns to step 1003, and the processes after step 1003 are repeatedly executed. On the other hand, if it is determined in the block mapping table 602 that the block number of the corresponding secondary storage is not 0, the process proceeds to step 1005.

In step 1005, the secondary storage block release means 116 (FIG. 1) releases the block of the corresponding secondary storage block number in the block mapping table 602, and The block number of the secondary storage of the block is set to 0.

Next, the secondary storage block securing means 115
The operation procedure of FIG. 1 will be described with reference to the flowchart of FIG. First, a secondary storage use status table 605 is obtained (step 1101). Next, a search is made for a secondary storage usage status table 605 whose usage status is “empty” (step 1102).

Next, in step 1103, it is determined whether or not a block whose usage status in the secondary storage usage status table 605 is "empty" is found. As a result, if "empty" is not found, it is determined that the memory space is insufficient (step 1105). On the other hand, if “empty” is found, “empty” in the secondary storage usage table 605
Is changed to “in use”, and the block number is returned to the task memory securing unit 113 (step 110).
4). When the processing of step 1104 or step 1105 ends, the present processing ends.

Next, secondary storage block releasing means 116
The operation procedure of FIG. 1 will be described with reference to the flowchart of FIG. First, the secondary storage use status table 605 is obtained (step 1201). Next, the use status of the entry corresponding to the block specified to be released by the task memory release means 114 is changed to "free" (step 1202). After that, the process ends.

As described above, according to the present embodiment, the following effects can be obtained. That is, it is possible to coexist an execution environment of an application requiring a large capacity memory while maintaining the performance of the embedded software. The reason is that, on an operating system operating in the direct mode, a function close to virtual memory can be partially provided for a necessary task, and this part can hold information multiplexed for each task. It is. That is, a plurality of tasks can share a predetermined memory space of the real memory. As a result, the memory can be partially multiplexed while operating in the direct mode.

Next, another embodiment to which the present invention is applied will be described. This embodiment does not have the block mapping table 601 indicating the real memory state in the embodiment described above. In the above-described embodiment, the contents in the actual memory are managed by the block mapping table 601 representing the actual memory state, and when the task is switched, the same data as the data used by the task after the switch is actually stored. If it remains in memory,
Again, it prevents recovery from secondary memory. In the present embodiment, this processing is omitted, and the implementation is simplified.

In this embodiment, in the following processing in the above-described embodiment, that is, in the operation of the task memory switching means 111 shown in the flowchart of FIG. A process of checking whether or not data remains (step 708) and a process of storing the block number of the recovered block in the block mapping table 601 of the real memory (step 71)
0) and the operation of the task memory allocating means 113 shown in the flowchart of FIG.
1 (step 906). In this embodiment, the same effects as in the previous embodiment can be obtained.

A program for executing the above-described processing is a CD-ROM (compact disc).
read only memory), DVD (dig)
It can be provided by being recorded on various recording media such as an italative disc, a floppy (registered trademark) disk, and a memory card. The program controls the operation of the computer, and the computer controlled by the program executes a predetermined process instructed by the program.

It should be noted that the configuration and operation of the above embodiment are examples, and it is needless to say that the configuration and operation can be appropriately changed without departing from the spirit of the present invention.

[0051]

As described above, according to the virtual storage method of the present invention, at least a part of the memory is mapped to the secondary storage for each task, and the task before switching is used when switching tasks. The contents of the memory that was saved are saved to the secondary storage mapping destination corresponding to the memory, and the contents of the memory used by the task after switching are restored from the secondary storage mapping destination corresponding to the memory. On an operating system that operates in the direct mode, an application can use a memory larger than the installed memory capacity, and an application that performs large-capacity data processing can be executed.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration example of an embodiment of an operating system of an embedded device to which the present invention is applied.

FIG. 2 is a diagram illustrating an example of a storage area of a secondary storage.

FIG. 3 is a diagram illustrating an example of a secondary storage use status table.

FIG. 4 is a diagram illustrating an example of a real memory;

FIG. 5 is a diagram illustrating an example of a block mapping table.

FIG. 6 is a diagram showing a correspondence relationship among a block mapping table of a real memory, a block mapping table of each task, and a secondary storage use status table.

FIG. 7 is a flowchart illustrating a task memory switching processing procedure.

FIG. 8 is a flowchart illustrating a processing procedure at the time of ending the task memory.

FIG. 9 is a flowchart for explaining a processing procedure when securing a task memory;

FIG. 10 is a flowchart illustrating a processing procedure when releasing a task memory.

FIG. 11 is a flowchart illustrating a processing procedure when a secondary storage block is secured.

FIG. 12 is a flowchart illustrating a processing procedure when a secondary storage block is released.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 Task dispatcher 102 Memory pool management 103 Secondary storage block use status management 111 Task memory switching means 112 Task memory ending means 113 Task memory securing means 114 Task memory releasing means 115 Secondary storage block securing means 116 Secondary storage block releasing means 601 604 Block mapping table 605 Secondary storage usage table

Claims (7)

[Claims] 1. A virtual storage method in an information processing apparatus comprising a memory and a secondary storage, wherein execution of a plurality of tasks is controlled by an operating system operating in a direct mode, wherein at least a part of the memory is A mapping step of mapping to the secondary storage for each task; and when switching the task, saving the contents of the memory used by the task before switching to a mapping destination of the secondary storage corresponding to the memory. A virtual storage method, comprising: a save step of saving the contents of the memory used by the task after switching from a mapping destination of the secondary storage corresponding to the memory. 2. A part of said memory and said secondary storage,
2. The virtual storage method according to claim 1, wherein the virtual storage method is divided into blocks each having a predetermined size and managed by block numbers assigned to the respective blocks. 3. Saving and restoring the memory at the time of the task switching based on a memory mapping table indicating a correspondence between each block of a part of the memory and a block of the secondary storage to which each block is mapped. 3. The virtual storage method according to claim 2, wherein is performed for each block. 4. A task memory virtually provided for each task is divided into blocks of a predetermined size, managed by block numbers assigned to each block, and each block of the task memory is Based on a task memory mapping table indicating the correspondence between the blocks and the blocks of the secondary storage mapped for each task, at the time of task switching, the content of the memory mapping table is changed to the task mapping table of the task after switching. 4. The virtual storage method according to claim 3, wherein the virtual storage method is rewritten with the following contents. 5. The task memory is mapped to the secondary storage when there is free space in the secondary storage, based on a usage status table indicating the usage status of each block of the secondary storage. The virtual storage method according to claim 4, wherein 6. An information processing apparatus comprising a memory and a secondary storage, wherein execution of a plurality of tasks is controlled by an operating system operating in a direct mode, wherein at least a part of the memory is provided for each task. Mapping means for mapping to secondary storage; and evacuation means for, when switching the task, saving the contents of the memory used by the task before switching to a mapping destination of the secondary storage corresponding to the memory. An information processing apparatus, comprising: recovery means for recovering the contents of the memory used by the task after switching from the mapping destination of the secondary storage corresponding to the memory. 7. A virtual storage control program in an information processing apparatus comprising a memory and a secondary storage, wherein execution of a plurality of tasks is controlled by an operating system operating in a direct mode, wherein at least a part of the memory is Mapping to the secondary storage for each task; and when switching the task, saving the contents of the memory used by the task before switching to a mapping destination of the secondary storage corresponding to the memory A virtual storage control program that causes the information processing apparatus to execute the following steps: and a step of restoring the contents of the memory used by the task after switching from the mapping destination of the secondary storage corresponding to the memory.