KR20110080479A - Flash memory storage device according to the multi-level buffer cache management policy and management method using the same - Google Patents

Abstract

PURPOSE: A memory management method according to a multi level buffer cache management policy is provided to offer a high hit ratio and a low flush number. CONSTITUTION: A monitor module(110) collects the state information of a page list comprising a page number, a reference frequency, a flag. An analysis module(120) analyzes the status information of the page list collected in the monitor module. According to the analyzed result of the analysis module, a cache policy module(130) updates the page list between step page lists. A buffer cache module(140) analyzes the page list update result of the cache policy module and selects and operates a replacement target page.

Description

FLASH MEMORY STORAGE DEVICE ACCORDING TO THE MULTI-LEVEL BUFFER CACHE MANAGEMENT POLICY AND MANAGEMENT METHOD USING THE SAME}

The present invention relates to a flash memory storage device for updating data according to a multi-level buffer cache management policy, and a data management method using the same.

Flash memory has made great progress in recent years, both quantitatively and qualitatively. Flash memory is used in personal and server computers as well as embedded and portable devices. Flash memory is expected to replace hard disks because of its light weight, fast read speed and impact resistance. There is so much demand now that there are no electronic devices that do not contain flash memory.

Flash memory has many of the above advantages, but there are also serious disadvantages to consider. First, it is not possible to overwrite the place when updating. In the case of a hard disk, the data is changed again, but the page cannot be rewritten before the flash memory is erased. In order to solve this problem, in a general flash memory, an update writes data to be updated in an empty area of the flash memory, and pages of previously written data are marked as invalid. Second, an additional operation called garbage collection is needed to allow the area marked invalid to be rewritten. Flash memory performs block-by-block operations, which adds the cost of copying invalid pages, so a good garbage collection policy is needed to reduce this additional cost. Third, the number of erase of flash memory is limited to 10,000 ~ 1,000,000 times. If the erase count of the flash memory is exceeded, the data written to the flash memory is not maintained properly and the data is not reliable. If the erase count of each block of the flash memory is not uniform, the life of the flash memory can be shortened. Therefore, a wear-leveling policy for maintaining the erase count of each block evenly is required.

In order to solve the above problems, the present invention is to provide a flash memory storage device for updating data according to a multi-level buffer cache management policy (Multu-Level Buffer Cache Management Policy) and a data management method using the same.

According to an aspect of the present invention, there is provided a flash memory storage device including: a monitor module for collecting status information of a page list including a page number, a reference frequency, and a flag; An analysis module for analyzing status information, a cache policy module for updating a page list among step-by-step page lists, and a page list update result of the cache policy module according to an analysis result of the analysis module, and selecting a page to be replaced; Contains a buffer cache module to operate on.

In addition, the buffer cache module selects a page to replace by analyzing a flag or reference frequency of the page list existing in the first step.

In addition, the cache policy module, according to the page list analysis result of the first stage, moves the page whose reference frequency exceeds the threshold to the page list of the second stage, and moves the page list to the page list of the second stage. Initialize the reference frequency of to 1.

In addition, when the number of pages remaining in the page list of the first step becomes 0 according to a result of page movement, the cache policy module moves the page list of the second step down to the page list of the first step.

The cache policy module merges the pages remaining in the first and second stages when the number of pages remaining in the page list of the first stage and the page list of the second stage becomes 1 according to the page movement result. To generate a new first page list.

In accordance with another aspect of the present invention, there is provided a method of managing a flash memory, including: a collecting step of collecting state information of a page list including a page number, a reference frequency, and a flag stored in a flash memory device; An analysis step of analyzing the status information of the page list, an update step of updating the page list between step-by-step page lists according to the analysis result, and a flag or reference frequency of the page list existing in the first step according to the update result An optional step of selecting a page to be analyzed and replaced is included.

In the updating step, the page frequency of the pages existing in the first step exceeding the threshold value is moved to the page list of the second step, and the reference frequency of the page moved to the page list of the second step is changed. Initialize to 1.

The flash memory storage device and the flash memory management method using the same according to at least one embodiment of the present invention configured as described above have the advantage of providing a high hit ratio and a low number of flushes. have.

1 is a block diagram of a flash memory storage device according to an embodiment of the present invention.
2 is a diagram illustrating a page list of a flash memory storage device according to an exemplary embodiment.
3 is a diagram illustrating an algorithm for selecting a replacement target according to an embodiment of the present invention.
4 illustrates a page list for updating a step-by-step page list according to an embodiment of the present invention.
5 is a diagram illustrating a page list generated by merging step-by-step page lists according to an embodiment of the present invention.
FIG. 6 is a view illustrating a hit ratio using a flash memory storage device according to an exemplary embodiment of the present invention. FIG.
FIG. 7 is a view illustrating a number of flush operations using a storage device of a flash memory according to an embodiment of the present invention. FIG.

Hereinafter, a flash memory storage device and a flash memory management method using the same will be described in more detail with reference to the accompanying drawings. Those skilled in the art to which the present invention pertains may refer to various embodiments of the configuration of the realistic broadcast system by referring to or modifying the drawings, but the present invention includes the various embodiments inferred by the present invention. And the technical features are not limited to the embodiment shown in the drawings below.

1 is a block diagram of a flash memory storage device according to an exemplary embodiment.

Referring to FIG. 1, the flash memory storage device 100 includes a monitor module 110, an analysis module 120, a cache policy module 130, a buffer cache module 140, and an interface module 150.

The monitor module 110, in order to collect cache state information and usage information of an application, state information of a page list including a page number (page #), a reference frequency (RC), and a flag. Collect it. The page number refers to information about a block loaded in the cache memory, and means a number set to distinguish each block. The reference frequency is a number representing the number of times the page is referred to. It is assumed that a highly referred page is likely to be referred to in the future according to a Least Frequently Used (LFU) policy, and that the referred page is not referred to in the future. It suggests whether or not it is possible to refer. The flag indicates whether data stored in the page has been updated in the cache memory, a clean flag for a page that is also updated for cache memory, and a dirty flag for a page that is not updated for cache memory. dirty flags).

The analysis module 120 analyzes state information of the page list collected by the monitor module 110 and extracts characteristics of an application program. In detail, the analysis module 120 analyzes the reference frequency numbers described for each page, and determines the reference number of the corresponding page. In addition, the analysis module 120 analyzes the flags described for each page to determine whether the data of the corresponding page is stored in the cache memory. The information analyzed by the analysis module 120 is then used to update the list in the cache storage module 130.

The cache policy module 130 updates the page list among the step-by-step page list to operate the policy optimized for the application according to the analysis result of the analysis module 120, so as to rank the highly referenced pages. Go to the page list of the step. In detail, the cache policy module 130 moves a page whose reference frequency exceeds a threshold to the page list of the second step according to the page list analysis result of the first step. Initializes the reference frequency of the page passed to the page list of to 1. When the number of pages remaining in the page list of the first step becomes 0 according to the moving result, the step is moved down from the page list of the second step to the page list of the first step. In addition, when the number of pages remaining in the page list of the first step and the page list of the second step becomes 1 according to the page movement result, the pages remaining in the first and second steps are merged to form a new first. Creates a page list of steps, while managing the list in multiple steps, while avoiding excessive growth of steps. In the case where the merge operation is performed as described above, a problem may occur in the reference frequency, so that the reference frequency is corrected after the merge. For example, when merging pages of multiple stages, the reference count of the uppermost page is maintained as it is, and the reference frequency of the pages of the lower stage can be made smaller. In this case, since the reference count of the uppermost page should be greater than or equal to 3, if it is smaller than 3, this is solved by adjusting the reference count of the lowermost step to 3 while reducing the reference count of the lower step. The page list of the first step and the second step is a page list attached step by step from the lowest list, and may include two or more plurality.

In order to optimize the buffer cache, the buffer cache module 140 selects a page to be replaced according to the page list update result of the cache policy module 130 and performs a page operation. In detail, the buffer cache module 140 may refer to the reference frequency or the flag in the page list of the first step according to the page update result of the cache policy module 130 to replace the page having the dirty flag with priority. Select to delay the dirty pages that are not stored in cache memory as much as possible. If all pages included in the page list of the first step correspond to the clean flag, the reference frequency is analyzed to select a page having a low reference frequency.

The interface module 150 performs a function of providing an input / output interface to the flash memory storage device and the file system.

2 is a diagram illustrating a page list of a flash memory storage device according to an exemplary embodiment.

Referring to FIG. 2, the page list includes a first step page list 210, a second step page list 220, and a third step page list 230, and each step page list includes a plurality of pages. Include. For example, the first step page list 210 includes a first page 211, a second page 212, and a third page 213. Each page 211 includes a page number 211A, a reference frequency 211B, and a flag 211C. When such a page list is shown, the flash memory storage device selects the third page 213 of the page list 210 of the first step having the lowest reference frequency among the clean flags as the page to be replaced. If the flags of all pages included in the page list 210 of the first step are dirty flags, the rightmost page having the lowest reference frequency will be selected as the page to be replaced.

3 is a diagram illustrating an algorithm for selecting a replacement target according to an embodiment of the present invention. Referring to FIG. 3, the algorithm for selecting the replacement page is represented by pseudo code. In this algorithm, the page corresponding to the clean flag is searched in reverse order, and the computational complexity of the algorithm becomes O (n).

4 is a diagram illustrating a page list for updating a step-by-step page list according to an embodiment of the present invention. Referring to FIG. 4, when the threshold value of the reference frequency of the list is set to 10, the second step is shown. If the reference frequency of one page 410 existing in the list of T is referred to two more times, it becomes equal to the limit value (S410). In this case, the page 410 having the same reference frequency as the threshold value is updated to the page of the third step, which is the page of the higher level, and the reference frequency is initialized to 0 again (S420).

5 is a diagram illustrating a page list generated by merging step-by-step page lists according to an embodiment of the present invention. Referring to FIG. 5, when updating a page list, a new higher level page movement may occur and the number of remaining pages may be reduced. In this case, an excessive increase in each step page may burden the flash memory storage device, thereby reducing the number of step pages. Specifically, when a page list update occurs, the number of pages managed by the list is checked while traversing the page lists of the next step from the top page list. If a list of managing pages is 1 is continuously detected, the pages are merged into one list to perform an operation. The merged page list is adjusted to the list step of the lowest level. In FIG. 5, the page 510 of the first step, the page 520 of the second step, and the page 530 of the third step have only one page remaining, so that the three pages are combined to form a new list 540. ), And in this case, the level of the newly created list is adjusted to the lowest level and becomes the page list of the first level. In the merger as described above, the reference number needs to be adjusted, and the page 520 of the second step and the page 510 of the first step are based on the reference number of the page 530 of the third step, which is the highest level. Adjust by decreasing the reference count of

FIG. 6 is a diagram illustrating a hit ratio using a flash memory storage device according to an exemplary embodiment of the present invention. Referring to FIG. 6, when analyzing the performance evaluation in the sequential access workload, it can be seen that the power ratio 610 of the flash memory according to an embodiment of the present invention is higher than that of the flash memory of another technique. . This difference can be seen that the smaller the size of the buffer cache appears higher.

7 is a diagram illustrating a number of flush operations using a storage device of a flash memory according to an embodiment of the present invention. Analyzing performance evaluation in sequential access workload, it can be seen that the number of flush operations 710 of the flash memory according to an embodiment of the present invention is 20% to 120% lower than the number of flush operations of the flash memory of another technique. Can be.

The above-described flash memory storage device and the flash memory management method using the same are not limited to the configuration and method of the above-described embodiments, but the embodiments may be modified in various ways so that various modifications may be made. Or some may be optionally combined.

100: flash memory storage device
110: monitor module
120: analysis module
130: cache policy module
140: buffer cache module
150: interface module

Claims (8)

A monitor module for collecting status information of a page list including a page number, a reference frequency and a flag;
An analysis module for analyzing state information of the page list collected by the monitor;
A cache policy module for updating a page list between step-by-step page lists according to an analysis result of the analysis module; And
And a buffer cache module for analyzing the page list update result of the cache policy module and selecting and calculating a page to be replaced.
The method of claim 1,
And the buffer cache module selects a page to be replaced by analyzing a flag or a reference frequency of the page list existing in the first step.
The method of claim 1,
The cache policy module moves a page whose reference frequency exceeds a threshold to the page list of the second step according to the page list analysis result of the first step, and references the page moved to the page list of the second step. Flash memory device, characterized in that to initialize the frequency to 1.
The method of claim 3, wherein
The cache policy module, when the number of pages remaining in the page list of the first step becomes 0 according to the result of page movement, moves the page list of the second step down to the page list of the first step. Flash memory storage device.
The method of claim 3, wherein
When the number of pages remaining in the page list of the first step and the page list of the second step becomes 1 according to the page movement result, the cache policy module merges the remaining pages in the first and second steps. Flash memory storage device, characterized in that for generating a page list of the first step.
A collecting step of collecting status information of a page list including a page number, a reference frequency, and a flag stored in the flash memory device;
An analyzing step of analyzing state information of the collected page list;
An update step of updating the page list between the step-by-step page list according to the analysis result; And
And selecting a page to be replaced by analyzing a flag or reference frequency of the page list existing in the first step according to the update result.
The method according to claim 6,
In the updating step, a page having a reference frequency exceeding a threshold value among pages existing in the first step is moved to the page list of the second step, and the reference frequency of the page moved to the page list of the second step is 1; Flash memory management method characterized in that the initialization.
The method of claim 7, wherein
In the updating step, if there are no pages remaining in the first step, the page list of the second step is set downward to the page list of the first step.

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