JPH06309220A - Memory control system - Google Patents

Abstract

PURPOSE:To provide the system which is high in the utilization efficiency of a memory address space and improves the execution efficiency of garbage collection by performing the garbage collection in the memory address space by a moving method first, and then performing subsequent collection by a lateral sliding method by link inversion if a copy space is deficient during the execution of the garbage collection. CONSTITUTION:Each of utilization space and a copy space is assigned by 1/2 first and normal processing other than the garbage collection is performed (step S3), and, for example, the garbage collection becomes necessary. Then the garbage collection by the moving method is started (step S4) and when the garbage collection normally ends (step S5), namely, when the amount of active cells matches an estimated amount or is less than the estimate amount, the garbage collection normally ends. When the garbage collection does not normally end in the step S5, on the other hand, the garbage collection is performed by the lateral sliding method by link inversion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a memory control system capable of efficiently implementing garbage collection in a computer system.

[0002]

2. Description of the Related Art Garbage collection is performed in order to collect unnecessary information in a memory address space. As algorithms for such garbage collection, there are "movement method" and "sideslip method by link inversion". . The move method is to divide the memory address space into two equal parts, and first store the information in only one of the partial spaces. When the free cell {unused cell (= area)} disappears, the root (link The cell that is reachable from the specific cell that is the starting point of, that is, the active cell is copied to the other subspace.

The skid method by link inversion is a method of collecting active cells at the end of the memory address space while maintaining the order of arrangement of the active cells, and has a feature that a stack is not used for marking. .

FIG. 2 is an explanatory diagram of the sideslip method by the link inversion. First, in the memory address space,
In (A), cell a is pointing to cell b. That is, cell a has a pointer to cell b. Here, when the cell a is to be moved in the direction of the arrow, this cell a can move freely. This is because the pointer to cell b does not change even if cell a is moved.

On the other hand, as shown in (B), the cell (here, cell a) pointed to by another cell (here, cell b) cannot move freely. That is, when the cell a is moved, the pointer of the cell b must be corrected, but the cell pointed to by another cell cannot be known because it is not known from which cell the cell is pointed. Is.

That is, when a certain cell is to be moved, it can be moved freely in the opposite direction of the pointer, but cannot be moved as it is in the same direction as the pointer.

Therefore, in the case as shown in FIG.
This is performed as shown in FIGS. 2 (C1) to (C3). First, (C
As shown in 1), the pointer is once reversed so that the pointer is in the direction opposite to the moving direction of the cell. It should be noted that this pointer replacement can be performed by scanning all areas once and confirming that the pointer of the cell b is the cell a.

In (C1), since the pointer is in the direction opposite to the moving direction of the cell, the cell a can be moved freely, and therefore, the cell a is moved to the memory address head block as the end of the memory address space. This state is (C2). Then, when the movement of the cell a is completed,
The memory address space is again scanned, and the pointer is reversed as shown in (C3), whereby the cell a can be moved even in the state shown in (B). In this way, in the skid method by link inversion, active cells are collected at the end of the memory address space (in the direction of the first memory address), and garbage collection is executed.

[0009]

The skid method by link inversion described above has a feature that a stack is not used for marking, but on the other hand, since the memory address space is scanned twice over the entire area. However, it has a drawback that the execution efficiency is not good. That is, when the amount of active cells is small, the "moving method" is advantageous.

However, in the case of the transfer method, since all active cells must be copied at the time of executing the garbage collection, the used space for normal access and the copy destination space have the same size. However, in general, when performing garbage collection, the amount of cells to be copied to the copy destination space is smaller than the amount of active cells in the normally used space, and from this perspective, in the case of the move method, due to the limitation of the memory address space. As a result, the number of times garbage collection is started increases, which causes a problem that system performance deteriorates. The present invention has been made to solve the above conventional problems, and an object of the present invention is to provide a memory control method that enables high utilization efficiency of a memory address space and also improves execution efficiency of garbage collection. To do.

[0011]

According to the memory control method of the present invention, when performing a garbage collection of a memory address space, first, the memory address space is divided into a used space for normal access and a copy destination space. It divides and executes by the moving method that performs garbage collection by copying the active cell of the used space to the copy destination space, and determines the division ratio of the used space and the copy destination space based on the result of the previous garbage collection. Then, if the copy-destination space runs short while performing the garbage collection of the memory address space by the migration method, the subsequent garbage collection is performed on the active cell while maintaining the order of the active cells. What to do with the sideslip method by link reversal gathering at the end of the address space It is an feature.

[0012]

In the memory control method of the present invention, when the garbage collection of the memory address space is performed, the moving method is first performed. At this time, the division ratio of the used space and the copy destination space is determined according to the amount of active cells copied in the previous garbage collection. After that, when the copy destination space is insufficient during execution of the garbage collection by the moving method, the subsequent garbage collection is performed by the sideslip method by the link inversion. Further, as a result of the executed garbage collection, for example, when the amount of active cells is more than half of the memory address space, the next garbage collection is performed by the skid method by link inversion from the beginning.

[0013]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a flow chart showing an embodiment of the memory control system of the present invention. Prior to this explanation, the memory address space in the conventional and this embodiment will be explained.

3A and 3B are explanatory views of the memory address space of the conventional example and the example. FIG. 3A shows the conventional example and FIG. 3B shows the present example. First, in order to make the cell space variable, the memory address space is divided into blocks (pages) and managed. Conventionally, as described above, the used space and the copy destination space in the memory address space are each 1/2.
One by one. In addition, the used space is a normal memory address space that is accessed when a cell is allocated and processing is performed after performing garbage collection. On the other hand, the copy destination space is a space where the active cell at the time of garbage collection is copied and becomes a used space after garbage collection, and is a space reserved without being used at the time of executing a normal process.

In the present embodiment, the division ratio between the copy destination space and the used space is variable, and the size of the copy destination space follows the estimation of the active cell amount. As an example of this estimation, the value obtained by adding 1 block (this value experimentally selects an arbitrary number of blocks) to the number of blocks required by the active cell at the time of garbage collection after the end of garbage collection. Estimated number of blocks. The estimated number of blocks shall not exceed 1/2 of the total number of blocks. In addition, the used space and the copy destination space are set alternately due to the occurrence of garbage collection. That is, after the garbage collection, a new copy destination space is set in the part of the original used space, and the other part is set as the used space.

Next, the memory control system of this embodiment will be described with reference to FIG. When the system starts operating (step S1), first, memory address space is allocated (step S2). In this case, initially, as in the conventional case, the used space and the copy destination space are allocated to each half.
After that, normal processing other than garbage collection is performed (step S3), and it is assumed that garbage collection becomes necessary. Thereby, the garbage collection (GC) by the moving method is started (step S4), and when this is normally completed (step S5), that is, when the amount of active cells matches the estimated amount, or when the estimated amount is less than or equal to the estimated amount, Garbage collection ends normally. afterwards,
The estimated number of blocks is newly determined according to the amount of copied active cells, the memory address space is divided again (step S6), and the process returns to step S3 to continue the normal processing.

FIG. 4 is an explanatory diagram showing this state. First, (a) is the state of the memory address space before the garbage collection in step S4 is started,
The shaded area in the usage space indicates the active cell. Then, the garbage collection is executed, all the active cells are copied to the copy destination space, and the normal termination is shown in the state of (b). After that, the number of estimated blocks is newly determined, and the state of (c) is obtained.

On the other hand, if the garbage collection does not end normally in step S5, the sideslip method by link reversal is used to perform garbage collection (step S).
7). That is, in the garbage collection by the moving method, if the amount of active cells is larger than the estimated amount of the copy destination space, the process does not end normally, and therefore it is necessary to copy the remaining active cells. However, since the copy destination space has already been used up, it is necessary to refill the used space and generate a block for the copy destination space. Therefore, the sideslip method by link inversion is used here.

Here, a point to be noted when performing the garbage collection by the skid method by link inversion is that the skid method is changed to the skid method during the moving method. At this time, since the pointer to the used space exists in the unswept area in the copy destination space, the sideslip method by link inversion is performed in the space including both this space and the used space.

FIG. 5 is an explanatory diagram in the case of shifting from the moving method to the sideslip method by link inversion. FIG. 5 is an explanatory diagram when the garbage collection does not end normally in step S5 in FIG. 1. First, FIG. 5A shows a state before the start of garbage collection by the moving method in step S4. Then, although the garbage collection is performed by the moving method, the copy destination space is insufficient, and the garbage collection is not normally completed by the moving method, and this state is shown in FIG. 5B. At this point, in the memory address space, a used space (hereinafter, referred to as an area A), an area that has already been swept in the copy destination space (hereinafter, referred to as an area B), and an unswept area (hereinafter, referred to as an area B) in the copy destination space. , Area C).

Here, there are a region A and a region C as regions where the garbage collection is not yet completed, and the skid method is applied to these regions. In the area B, the side-slip method is not necessary because all the pointers point to the copy destination space. Therefore, the area C and the area A are regarded as continuous areas, and the garbage collection is started on the area by the skid method. This state is shown in FIG. 5 (c). At this time, the starting point of the skid method is the start address of the area B.

After that, when the garbage collection by the skidding method is normally completed (step S8 in FIG. 1), the process proceeds to step S6, and the memory address space is reallocated. This state is shown in FIGS. 5 (d) and 5 (e). That is, FIG. 5D shows a state where the garbage collection is completed. Then, as shown in FIG. 5E, this time, the space to which the active cell has been copied is set as a new utilization space, and the next copy destination space is estimated based on the copied active cell amount.

Further, in FIG. 1, when the garbage collection is normally completed in step S8, the number of active cells in the copy destination space is 1/2 of the total number of blocks.
(This value can be set arbitrarily experimentally)
If it exceeds, the next sideways garbage collection uses the "side slip method by link inversion" from the beginning. And
In such a case, it is not necessary to secure the copy destination space. On the other hand, in step S8, if the garbage collection is not normally completed, that is, if the number of active cells exceeds 4/5 of the total number of blocks (this value may also be determined experimentally). , Abnormally terminate garbage collection because it cannot execute processing due to lack of memory.

As described above, in the above embodiment, the memory address space is first garbage-collected by the migration method, and the division ratio of the used space and the copy-destination space is determined based on the result of the previous garbage collection. If the copy destination space is insufficient while performing the garbage collection by the move method after performing the determination, the subsequent garbage collection is performed by the sideslip method by link inversion, and the active cell amount is determined as the result of the executed garbage collection. If there is more than half of the memory address space, the next garbage collection is performed by the sideslip method by link inversion from the beginning. The number of times garbage collection is started can be reduced. Further, it is possible to perform garbage collection when there are 1/2 or more active cells in the entire memory address space, which is impossible with the "movement method".

[0025]

As described above, according to the memory control method of the present invention, the garbage collection of the memory address space is first performed by the migration method, and the division ratio of the used space and the copy destination space is made variable, After that, if the destination space runs out while performing garbage collection,
Since the subsequent garbage collection is performed by the sideslip method by link inversion, the number of times garbage collection is activated due to the limitation of the memory address space in the garbage collection by the move method is reduced and the performance of the system is improved. You can

[Brief description of drawings]

FIG. 1 is a flowchart of a memory control method of the present invention.

FIG. 2 is an explanatory diagram of a skid method by link inversion.

FIG. 3 is an explanatory diagram of a memory address space according to the related art and the present invention.

FIG. 4 is an explanatory diagram in the case where the garbage collection by the moving method in the memory control system of the present invention is normally completed.

FIG. 5 is an explanatory diagram of a case where garbage collection is performed by a sideslip method by link inversion in the memory control method of the present invention.

Claims (1)

[Claims] 1. When performing garbage collection of a memory address space, first, the memory address space is divided into a used space for normal access and a copy destination space, and an active cell of the used space is copied. It is executed by the move method that performs garbage collection by copying to the destination space, and the division ratio of the used space and the copy destination space is determined based on the result of the previous garbage collection, and then the memory address space by the move method. If the copy destination space is insufficient while executing the garbage collection of, the subsequent garbage collection is performed by the side-slip method by link inversion that collects the active cells at the end of the memory address space while keeping the order of the active cells. A memory control method characterized by performing.