JP2012164129A - Buffer cache management method, buffer cache management device and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mechanism for managing data on a plurality of storage devices whose physical sector sizes are different, without dividing a buffer cache area for each of the storage devices.SOLUTION: A buffer cache management system (a buffer cache management device) 103 for managing a buffer cache 108 which holds data on a plurality of storage devices (105-107) having different sector sizes, manages a memory area used for the buffer cache 108 with the biggest sector size among the plurality of storage devices (105-107) as a basic management unit and manages a block for storing the data by further dividing the basic management unit internally, according to the size of a sector to be accessed.

Description

  The present invention relates to a buffer cache management method, a buffer cache management device, and a program for managing a buffer cache that holds data on a plurality of storage devices having different sector sizes in a file system.

  A file system is a method for managing data recorded in a storage device, software for management, management area and management information provided in a storage medium.

  This file system often has a mechanism called a buffer cache. This is because data read from the storage device or data to be written to the storage device is temporarily placed in a memory area called a buffer cache, speeding up access using the locality of reference, reducing the number of accesses to the storage device, This is for speeding up by prefetching.

  A storage device generally uses a fixed-size physically continuous area called a sector as a minimum unit, and a file system records and reproduces data in this unit. In general, the size is defined as a power of two.

  The sector size is 512 bytes in typical storage devices such as hard disks and SD cards. In addition, there are media having a sector size of 1K (1024) bytes or 2K bytes. For this reason, there is a request to be able to achieve compatibility between 512 bytes and these large-capacity sector sizes.

  In the case of handling data on storage devices having different physical sector sizes, a method for absorbing the difference between the sector sizes of the OS (file system) and the storage device has already been proposed (for example, Patent Document 1 below, Patent Document 2, the following Patent Document 3, the following Patent Document 4, and the like).

JP-A-4-165527 US Pat. No. 5,485,439 Japanese Patent Laid-Open No. 4-14127 JP-A-9-146710

  However, in the conventional method described above, when a plurality of storage devices having different sector sizes are to be handled, the data in the buffer cache is synchronized every time the storage device to be accessed is switched, or the buffer cache is changed according to the number of storage devices. It is necessary to divide the area. For this reason, there are problems such as “cannot be handled completely at the same time” and “inefficient use of buffer cache”.

  The present invention has been made in view of such problems, and provides a mechanism for managing data on a plurality of storage devices having different physical sector sizes without dividing the buffer cache area for each storage device. For the purpose.

The buffer cache management method of the present invention is a buffer cache management method by a buffer cache management device for managing buffer caches that hold data on a plurality of storage devices having different sector sizes, and is used for the buffer cache. A basic management unit management step for managing a memory area using a maximum sector size of the plurality of storage devices as a basic management unit, and a partition for storing the data according to the size of the sector to be accessed. And a division management step for further dividing and managing them internally.
The present invention also includes a buffer cache management apparatus that executes the above-described buffer cache management method, and a program for causing a computer to execute the buffer cache management method.

  According to the present invention, it is possible to simultaneously handle (manage) data on a plurality of storage devices having different physical sector sizes without dividing the buffer cache area for each storage device. Can be improved.

1 is a schematic diagram illustrating an example of an overall configuration including a file system for managing data on a storage device according to an embodiment of the present invention. It is a flowchart which shows embodiment of this invention and shows an example of the process sequence of the acquisition method of the largest physical sector size. It is a flowchart which shows embodiment of this invention and shows an example of the buffer cache method. It is a schematic diagram which shows Example 1 of this invention and shows an example of the state transition of a buffer cache. It is a schematic diagram which shows Example 1 of this invention and shows an example of the state transition of a buffer cache. It is a schematic diagram which shows Example 1 of this invention and shows an example of the state transition of a buffer cache. It is a schematic diagram which shows Example 1 of this invention and shows an example of the state transition of a buffer cache. It is a schematic diagram which shows an example of the LRU order of a buffer, and a replacement object block. It is a schematic diagram which shows an example of the hardware constitutions of the buffer cache management system (buffer cache management apparatus) shown in FIG.

  Hereinafter, embodiments (embodiments) for carrying out the present invention will be described with reference to the drawings.

Here, embodiments of a buffer cache management system (buffer cache management apparatus), a buffer cache management method, and a program according to the present invention will be described with reference to the drawings.
First, FIG. 1 is a schematic diagram showing an example of an overall configuration including a file system for managing data on a storage device according to an embodiment of the present invention.

  In FIG. 1, an application 101 acquires data from a storage device (105 to 107) by a driver 104 via a file system 102 when data in a connected storage device is to be used in a program. However, if the target data is already cached in the buffer cache 108 by the buffer cache management system 103 included in the file system 102, the storage device is not accessed and the data is acquired from the buffer cache 108.

  In this embodiment, it is assumed that the storage devices 105, 106, and 107 in FIG. 1 are connected to “a plurality of storage devices having different physical sector sizes”. The physical sector size is 512 bytes, 1K, respectively. It is a storage device different from byte, 2K byte. The data in these storage devices is managed without dividing the area of the buffer cache 108 into “for each storage device”.

A buffer cache management system (buffer cache management device: the same applies hereinafter) 103 is for managing a buffer cache 108 that holds data on a plurality of storage devices having different sector sizes.
Specifically, the buffer cache management system 103 manages the memory area used for the buffer cache 108 with the maximum sector size of a plurality of storage devices as a basic management unit (basic management unit management step). In the example shown in FIG. 1, 2 Kbytes are the basic management unit. Then, the buffer cache management system 103 manages the partition for storing the data by further dividing the basic management unit (2 K bytes in the example shown in FIG. 1) further internally according to the size of the sector to be accessed ( Split management step).

  As described above, the buffer cache 108 is managed with the largest physical sector size among the connected storage devices. This maximum physical sector size is stored in the maximum sector size storage area 109 in the buffer cache management system 103. The method for obtaining the maximum physical sector size follows the flowchart of FIG.

  FIG. 2 is a flowchart illustrating an example of a processing procedure of the method for obtaining the maximum physical sector size according to the embodiment of this invention.

  First, in step S201, for example, the buffer cache management system 103 initializes the maximum sector size (maximum physical sector size) to zero.

  Subsequently, in step S202, for example, the buffer cache management system 103 recognizes one connected storage device.

  Subsequently, in step S203, for example, the buffer cache management system 103 acquires the sector size of the storage device recognized in step S202.

  Subsequently, in step S204, for example, the buffer cache management system 103 determines whether or not the sector size acquired in step S203 is larger than the current maximum sector size (maximum physical sector size). As a result of the determination, if the sector size acquired in step S203 is larger than the current maximum sector size (maximum physical sector size), the process proceeds to step S205.

  In step S205, for example, the buffer cache management system 103 updates the sector size acquired in step S203 as the maximum sector size (maximum physical sector size).

  When the process of step S205 is completed, or when the sector size acquired in step S203 in step S204 is not larger than the current maximum sector size (maximum physical sector size), the process proceeds to step S206.

  In step S206, for example, the buffer cache management system 103 determines whether the sector sizes of all the storage devices have been acquired. As a result of the determination, if the sector sizes of all the storage devices have not yet been acquired, the process proceeds to step S207.

  In step S207, for example, the buffer cache management system 103 recognizes the next storage device that has not acquired the sector size. Then, it returns to step S203 and performs the process after step S203. That is, the processes in steps S203 to S205 are repeated until the sector sizes of all the storage devices are acquired, and the maximum sector size (maximum physical sector size) is obtained.

  On the other hand, if the result of determination in step S206 is that the sector sizes of all storage devices have been acquired, the processing of the flowchart of FIG.

  Therefore, in the case of FIG. 1, since the physical sector size of the storage device 107 is the largest at 2 Kbytes, the buffer cache 108 by the buffer cache management system 103 is managed in 2 Kbytes as a basic unit. At this time, the buffer area for every 2 K bytes is called a “buffer block”.

If there is no target data in the buffer cache 108, a cache is generated. The method for caching the data follows the flowchart of FIG.
FIG. 3 is a flowchart illustrating an example of the buffer cache method according to the embodiment of this invention.
The following [Embodiment 1] to [Embodiment 3] explain the flowchart corresponding to each step of the flowchart of FIG.
The buffer cache management system 103 in the following embodiment is executed by the information processing apparatus (buffer cache management apparatus) shown in FIG. In addition, a program that causes the CPU 910 to execute the processing of the flowcharts described in the embodiments described later is stored in the ROM 930. Then, when the program is executed, the program in the ROM 930 is read into the RAM 920 so that the CPU 910 can process it. Here, reference numeral 950 denotes a bus, which exchanges data of the ROM 930, the RAM 920, the CPU 910, and the HDD 940. The HDD 940 is a storage device and is a target whose sector size is managed by the CPU 910. Although not shown, the storage device managed by the file system may be a flash memory, an SSD (solid state disk), or the like in addition to the HDD (hard disk drive). The HDD (storage device) 940 may be detachable.

  When data is read into the buffer cache 108, in the free buffer search step in step S301, for example, the buffer cache management system 103 determines whether there is a free buffer on the cache buffer having the same size as the sector to be accessed. If it is determined that there is an empty buffer on the cache buffer having the same size as the sector to be accessed, the process proceeds to the sector cache step of step S310. When proceeding to the sector cache step of step S310, for example, the buffer cache management system 103 caches the data in an empty buffer having the same size as the sector size, and ends the process.

FIG. 4 shows the state transition of the buffer cache at this time.
FIG. 4 is a schematic diagram illustrating an example of state transition of the buffer cache according to the first embodiment of this invention. When the initial state is the buffer cache 402, the sector 401 to be accessed is cached in the buffer 404 closest to the head among the empty buffers having the same sector size as the sector 401 to be accessed (see the buffer cache 403).

Here, it returns to description of FIG. 3 again.
In the empty buffer search step in step S301, if an empty buffer on the cache buffer having the same size as the sector to be accessed is not searched, the process proceeds to an empty buffer block search step in step S302.

Subsequently, in the empty buffer block search step in step S302, for example, the buffer cache management system 103 determines whether there is an empty area of the buffer block. If the result of this determination is that there is a free space in the buffer block, the process proceeds to the buffer block dividing step in step S308.
In the buffer block dividing step of step S308, for example, the buffer cache management system 103 generates a free buffer by dividing the management size of the searched free buffer block into the sector size to be accessed. Thereafter, the process proceeds to the sector cache step of step S310. For example, the buffer cache management system 103 caches data in an empty buffer having the same size as the sector size, and ends the process.

FIG. 5 shows the state transition of the buffer cache at this time.
FIG. 5 is a schematic diagram illustrating an example of state transition of the buffer cache according to the first embodiment of this invention. When the initial state is the buffer cache 502, the empty buffer block 505 is divided by the sector size of the sector 501 to be accessed, and a state like the buffer cache 503 is obtained. Thereafter, the sector 501 to be accessed is cached in the buffer closest to the top of the free buffers divided as in the buffer cache 504.

Here, it returns to description of FIG. 3 again.
If there is no free space in the buffer block in the free buffer block search step in step S302, the process proceeds to the replacement target buffer determination step in step S303.
When proceeding to the replacement target buffer determination step in step S303, for example, the buffer cache management system 103 determines a replacement target buffer by an algorithm such as LRU.

Subsequently, in the buffer size comparison step in step S304, for example, the buffer cache management system 103 determines whether or not the size of the replacement target buffer is different from the size of the sector to be accessed. If the size of the replacement target buffer is different from the size of the sector to be accessed as a result of this determination, the process proceeds to the replacement target buffer block determination step in step S305.
When proceeding to the replacement target buffer block determination step in step S305, for example, the buffer cache management system 103 newly determines a replacement target buffer block in order to perform synchronization in the buffer block.

  Subsequently, in the buffer block synchronization step in step S306, for example, the buffer cache management system 103 synchronizes the replacement target buffer block determined in the replacement target buffer block determination step in step S305 with the storage device, and frees up the buffer block. A buffer block.

  Subsequently, in the buffer block combining step of step S307, for example, the buffer cache management system 103 returns the management unit of the buffer block synchronized in the buffer block synchronization step of step S306 to the buffer block size.

  Subsequently, in the buffer block dividing step of step S308, for example, the buffer cache management system 103 generates a free buffer by dividing the management size of the searched free buffer block into the sector size to be accessed. Thereafter, the process proceeds to the sector cache step of step S310. For example, the buffer cache management system 103 caches data in an empty buffer having the same size as the sector size, and ends the process.

FIG. 6 shows the state transition of the buffer cache at this time.
FIG. 6 is a schematic diagram illustrating an example of state transition of the buffer cache according to the first embodiment of this invention. When the initial state is the buffer cache 602, the replacement target buffer determined by the LRU is set to 607. When the sizes of the replacement target buffer 607 and the read data 601 are compared, the sizes are different. Therefore, in order to execute replacement in units of buffer blocks, the replacement target buffer block is determined in step S305.

  In the replacement target buffer block determination step in step S305, the LRU ordering for each buffer is used. Specifically, a representative value of the LRU order is set for each buffer block, and the replacement target is determined based on the representative value. However, the LRU ordering used here is a buffer that has been used for a longer time as the LRU order number is smaller.

  In the present invention, the representative value can be obtained by “representing the smallest (older) value in the block as a representative value”, “representing the largest (newer) value in the block as a representative value”, “ Three types of “take an average value as a representative value” are proposed. In the first embodiment, a method of “making the smallest (older) value in a block the representative value” will be described.

Here, FIG. 8 is a schematic diagram illustrating an example of the LRU order of the buffers and the replacement target block.
801 in FIG. 8 indicates the LRU order of each buffer in the buffer cache 602 in FIG. At this time, if the method of taking the representative value of the buffer block is performed by the method of “using the smallest (oldest) value in the block as the representative value”, the representative value of each buffer block is a numerical value such as 802 in FIG. become. As a result, the block 805 in FIG. 8 (606 in FIG. 6) having the smallest representative value among the blocks 802 in FIG. 8 is selected as the replacement target buffer block.

  When the buffer block to be replaced is selected, the block is synchronized with the block as indicated by reference numeral 604 in FIG. At this time, the management unit returns to the block size as in the state 603 in FIG. 6, and the synchronized block is regarded as an empty buffer block.

  The generated empty buffer block is divided by the sector size of the sector 601 to be accessed, and a state like 605 is obtained. Thereafter, the sector 601 to be accessed is cached in the buffer closest to the head among the divided buffers as in the state 606.

Here, it returns to description of FIG. 3 again.
If it is determined in the free buffer size comparison step in step S304 that the size of the replacement target buffer and the size of the sector to be accessed are the same, the process proceeds to the buffer synchronization step in step S309.
When proceeding to the buffer synchronization step of step S309, for example, the buffer cache management system 103 synchronizes the replacement target buffer with the storage device and sets the buffer as an empty buffer. Thereafter, the process proceeds to the sector cache step of step S310. For example, the buffer cache management system 103 caches data in an empty buffer having the same size as the sector size, and ends the process.

FIG. 7 shows the state transition of the buffer cache at this time.
FIG. 7 is a schematic diagram illustrating an example of state transition of the buffer cache according to the first embodiment of this invention. If the initial state is the buffer cache 702, the replacement target buffer determined by the LRU is set to 706. When the sizes of the replacement target buffer 706 and the read data 701 are compared with each other, the sizes are the same, so the replacement is performed in units of buffers.

  When the replacement target buffer is selected, the buffer is synchronized as in 704. At this time, as in the state of the buffer cache 703, the synchronized buffer is regarded as an empty buffer. Thereafter, the sector 701 to be accessed is synchronized as in the state of the buffer cache 705 and cached in the buffer that has become free.

  In the second embodiment, a case will be described in which the replacement target buffer block determination step in step S305 of the first embodiment is a method in which “the largest (new) value in a block is used as a representative value”.

  801 in FIG. 8 represents the LRU order of each buffer in the buffer cache 602 in FIG. At this time, if the method of taking the representative value of the buffer block is performed by the method of “using the largest (new) value in the block as the representative value”, the representative value of each buffer block is a numerical value such as 803 in FIG. become. As a result, the block 806 in FIG. 8, which has the smallest representative value among the blocks 803 in FIG. 8, is selected as the replacement target buffer block.

  Compared with the first embodiment, this method has an advantage that a recently read buffer is not easily replaced.

  After the replacement target buffer block is selected, the block is synchronized with the block in the same manner as in the first embodiment. At this time, the management unit returns to the block size, and the synchronized block is regarded as an empty buffer block.

  The generated empty buffer block is divided by the sector size of the sector 601 to be accessed, and then the sector 601 to be accessed is cached in the buffer closest to the head among the divided buffers.

  In the third embodiment, a case will be described in which the replacement target buffer block determination step in step S305 of the first embodiment is a method of “taking an average value in a block as a representative value”.

  801 in FIG. 8 represents the LRU order of each buffer in the buffer cache 602 in FIG. At this time, if the method of obtaining the representative value of the buffer block is performed by the method of “taking the average value in the block as the representative value”, the representative value of each buffer block becomes a numerical value such as 804 in FIG. As a result, the block 807 in FIG. 8, which has the smallest representative value among the blocks 804 in FIG. 8, is selected as the replacement target buffer block.

  After the replacement target buffer block is selected, the block is synchronized with the block in the same manner as in the first embodiment. At this time, the management unit returns to the block size, and the synchronized block is regarded as an empty buffer block.

  The generated empty buffer block is divided by the sector size of the sector 601 to be accessed. Thereafter, the sector 601 to be accessed is cached in the buffer closest to the head among the divided buffers.

(Other embodiments)
The present invention can also be realized by executing the following processing.
That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.
This program and a computer-readable recording medium storing the program are included in the present invention.

101 application, 102 file system, 103 buffer cache management system, 104 driver, 105-107 storage device, 108 buffer cache, 109 maximum sector size storage area

Claims (10)

A buffer cache management method by a buffer cache management device for managing a buffer cache for holding data on a plurality of storage devices having different sector sizes,
A basic management unit management step of managing a memory area used for the buffer cache as a basic management unit of a maximum sector size of the plurality of storage devices;
A buffer cache management method comprising: a partition management step for further dividing and partitioning the basic management unit internally according to the size of a sector to be accessed.   2. The buffer cache management method according to claim 1, further comprising an empty buffer search step of searching for an empty buffer on a cache buffer having the same size as the size of the sector to be accessed.   3. The empty buffer block searching step of searching for an empty area in a buffer block when there is no empty buffer having the same size as a sector to be accessed in the empty buffer searching step. Buffer cache management method. If there is no empty buffer block in the empty buffer block search step, a replacement target buffer determination step for determining a replacement target buffer by an algorithm including LRU;
4. The buffer cache management method according to claim 3, further comprising: a buffer size comparison step for comparing the replacement target buffer determined in the replacement target buffer determination step with the size of the sector to be accessed. If the size of the sector to be accessed differs from the replacement target buffer in the buffer size comparison step, a replacement target buffer block determination step for newly determining a replacement target buffer block in order to perform synchronization with the buffer block;
A buffer block synchronization step in which the replacement target buffer block determined in the replacement target buffer block determination step is synchronized with a storage device and the buffer block is an empty buffer block;
5. The buffer cache management method according to claim 4, further comprising: a buffer block combining step for returning a unit of management of the buffer blocks synchronized in the buffer block synchronization step to a buffer block size.   A buffer block dividing step of generating an empty buffer by dividing the management size of the empty buffer block searched by the empty buffer block searching step or the empty buffer block synchronized by the buffer block synchronizing step into the size of the sector to be accessed; 6. The buffer cache management method according to claim 5, further comprising:   When the size of the sector to be accessed is the same as the replacement target buffer in the buffer size comparison step, the buffer size comparison step further includes a buffer synchronization step of synchronizing the replacement target buffer with the storage device and setting the buffer as an empty buffer. The buffer cache management method according to claim 6.   A sector that caches a sector to be accessed in an empty buffer having the same size as the sector to be accessed searched in the empty buffer search step, an empty buffer generated in the buffer block dividing step, or an empty buffer generated in the buffer synchronization step The buffer cache management method according to claim 7, further comprising a cache step. A buffer cache management device for managing a buffer cache for holding data on a plurality of storage devices having different sector sizes,
Basic management unit management means for managing a memory area used for the buffer cache as a basic management unit of a maximum sector size of the plurality of storage devices;
A buffer cache management apparatus comprising: partition management means for managing a partition storing the data by further dividing the basic management unit internally according to the size of a sector to be accessed. A program for causing a computer to execute a buffer cache management method by a buffer cache management device for managing a buffer cache for holding data on a plurality of storage devices having different sector sizes,
A basic management unit management step of managing a memory area used for the buffer cache as a basic management unit of a maximum sector size of the plurality of storage devices;
A program for causing a computer to execute a division management step for further dividing and managing the basic management unit in accordance with the size of a sector to be accessed.

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