KR100908637B1 - How to manage data in flash memory - Google Patents

Abstract

A method for managing data in flash memory is disclosed. Priority flags are assigned to each page allocated on the buffer to minimize the number of programming times of pages in flash memory. By assigning a priority flag, each page is classified into a case where data can be recorded and a page that cannot be written and can be deported. Also, a page newly added to the empty space list is not set as the first page of the empty space list. Therefore, data can be recorded until there is no empty space in the page where the data is recorded. A distinct priority flag is set for a page where no free space exists and is expelled from the buffer by subsequent operations.

Description

Data management method of flash memory {Method of Managing Data of Flash Memory}

The present invention relates to a method for managing data in a flash memory, and more particularly, to a method for managing data through a minimal programming operation at the time of data update.

The flash memory is a kind of nonvolatile memory, and the stored data does not disappear even when power is cut off. Such a flash memory is divided into NAND flash memory and Noah flash memory.

In particular, the NAND flash memory consists of a cell array, and the cell array consists of a plurality of blocks. In addition, each block consists of a plurality of pages. Flash memory operation is divided into read, program, and erase operations. In particular, in the hardware structure of the NAND flash memory, erase operations are performed in units of blocks, and programming and read operations are performed in units of pages. That is, since the erase operation and the programming operation are different from each other, management of data related thereto is performed separately. For example, in order to use a flash memory as a hard disk, an address mapping operation for managing physical and logical addresses of data to be recorded independently is required.

In addition, in the case of NAND flash memory, programming is performed through hot-carrier injection, and erasing is performed by using a Fowler-Nordheim (F-N) tunneling phenomenon. In addition, the read operation is performed by detecting a change in the threshold voltage of each cell. Therefore, the programming operation is slower than the read operation.

If data is to be updated in a flash memory, an erase operation must be performed first, unlike a conventional DRAM. That is, when updating an existing page with new data, it is necessary to erase the block to which the page in which the existing data is programmed belongs and program the new data in the corresponding page. In particular, the erase operation is an operation in which the overhead of the flash memory is very large. In general, the number of erase operations guaranteed by the manufacturer of the flash memory is limited to 100,000 or less. In order to minimize such erase operations to improve the operating life of the flash memory, the number of programming operations should be reduced. This is generally because an erase operation must be preceded before programming.

The data management method stored in the flash memory is a data structure that determines the insertion, deletion, placement, and the like of data. There is a non-clustering method of managing such data. The non-clustering method is a method of storing data in a page in which empty space exists without considering key values of data to be recorded. In general, data is stored in the first page of pages in which empty space is determined to exist. In addition, pages determined to have free space are managed by a free space list.

1 is a conceptual diagram illustrating a conventional empty space list.

Referring to FIG. 1, the pages managed by the empty space list are in the order of page 1, page 2, page 3, and page 4. If data stored in page 1 is deleted, new empty space is generated in page 1. Therefore, page 1 should be added to the empty space list. Page 1 is then added to the beginning of the free space list. Also, when new data is added, the added data is stored in page 1, which is the first page of the empty space list.

2 is a flowchart for explaining a conventional non-clustering method when there is an insertion of data.

Referring to FIG. 2, when data to be inserted is generated (S10), it is checked whether a page into which new data is to be inserted exists in the buffer (S20). The buffer serves to compensate for the speed difference between the processor and the memory. Therefore, a portion of the main memory of the computer may be used as a buffer, or a memory added separately in the flash memory may be used as a buffer.

In addition, the page present on the buffer refers to the specific address constituting the corresponding page of the flash memory and the data stored in the specific address, rather than the actual page of the flash memory on the buffer. That is, the buffer adds or deletes data appropriate to the address of the corresponding page in order to write data to the page of the actual flash memory.

Subsequently, when the corresponding page exists in the buffer, new data is stored in the page without additional processing (S30).

If the corresponding page does not exist in the buffer, it is necessary to load the page in the buffer. In other words, it is necessary to set the capacity of the memory page in the buffer. At this time, it is determined whether there is a space for setting a page corresponding to the buffer (S40).

If there is enough space to set the page corresponding to the buffer, the corresponding page is set in the buffer (S50), and new data is written to the page (S30).

If there is not enough space in the buffer, a process of flushing a specific page from the buffer is necessary to free up space in the buffer. In order to be deported, an operation of selecting a page to be deported must first be performed. The algorithm for selecting a page to be deported is called a buffer replacement algorithm, and the deported page is called a victim page. When the victim page is selected (S60), it is checked whether the contents of the victim page are changed (S70).

If there is no change in the content of the victim page, the victim page is expelled from the buffer and a new page is set in the buffer (S50).

In addition, when there is a change in the content of the victim page selected through the buffer replacement algorithm, the data of the victim page is recorded in the corresponding page of the flash memory through a programming operation (S80). After the data of the victim page is reflected in the flash memory, the victim page is expelled from the buffer, and a new page is allocated to the buffer (S50).

However, although the non-clustering method described above can write more data to a page, a case of performing a programming operation occurs. This is because the existing buffer replacement algorithm does not consider the size of the empty space in the page and selects the victim page despite the empty space.

3A to 3F are conceptual views illustrating a process of performing a programming operation through a conventional buffer replacement algorithm.

Referring to FIG. 3A, data is inserted into page 1 set in the buffer 100. That is, when page 1 is loaded into the buffer through a read operation on page 1 of the flash memory 120, the data is inserted into the page 1 in the buffer 100. If page 1 of the buffer 100 is selected as the victim page, a programming operation for the flash memory 120 is performed as shown in FIG. 3B. When a programming operation is performed to write data of page 1 to flash memory 120, page 1 allocated to buffer 100 is deleted. If an empty space is generated in page 3 and data is recorded therein, page 3 is loaded into the buffer 100 as shown in FIG. 3C.

In addition, when empty space exists in page 1, new data may be recorded in page 1. Accordingly, as shown in FIG. 3D, page 1 of the flash memory 120 is returned to the buffer 100 through a read operation, and new data is written to page 1 of the buffer 100. After storing data in page 1 of buffer 100, if page 1 is selected as the victim page, a programming operation for page 1 should be performed again, as shown in FIG. 3E. Subsequently, when an empty space is generated in page 3 as shown in FIG. 3F and data must be written in the corresponding page, the area of page 3 of the flash memory 120 is set through a read operation in the buffer 100.

As described above, in the non-clustering method, a page programming operation may occur as many times as data is inserted. This frequent programming operation delays the time for writing data to the buffer and increases the erase operation in the flash memory, thereby shortening the life of the flash memory.

To solve this problem, as much data as possible is inserted into a page into which data is inserted, and then a buffer replacement algorithm for performing a programming operation will be requested.

An object of the present invention to solve the above problems is to provide a data management method of a flash memory that can minimize the number of programming operations of the data.

According to an aspect of the present invention, there is provided a method of managing page-allocated data in a flash memory, the method comprising: setting a priority flag on a page allocated on a buffer; Selecting a victim by reflecting the priority flag; And a step of avoiding the setting of the newly generated empty space as the first page of the empty space list and adding the new page.

According to the present invention, a programming operation should be performed after inserting as much data as possible in a page into which data is inserted in a flash memory having a large load due to a programming operation and an erase operation. Therefore, the data is managed so that no blank space is generated in accordance with data recording on each page. This reduces the number of programming operations, and reducing the number of programming leads to the reduction of erase operations. This reduction in erase operation extends the life of the flash memory.

As the inventive concept allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the text. However, this is not intended to limit the present invention to a specific disclosed form, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention. In describing the drawings, similar reference numerals are used for similar elements.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in the commonly used dictionaries should be construed as having meanings consistent with the meanings in the context of the related art and shall not be construed in ideal or excessively formal meanings unless expressly defined in this application. Do not.

Hereinafter, with reference to the accompanying drawings, it will be described in detail a preferred embodiment of the present invention.

Example

In the buffer replacement algorithm according to the present invention, a priority flag is set on a page into which data is inserted. Therefore, the priority flag is considered when selecting the victim page.

The priority flag indicates a page into which data is inserted or a page which may be selected and deported to a victim page. That is, a priority flag is set by distinguishing between a case where an empty space exists and a case where there is no empty space in each page set on the buffer.

For example, when new data is inserted into a specific page, the priority flag of the corresponding page is set to one. The page with the priority flag set to 1 is excluded in the process of selecting the victim page. If there is no more space for inserting data on the page, the priority flag of the page is set to zero. A page whose priority flag is set to 0 is expelled from the buffer when it is necessary to allocate a new page without sufficient space in the buffer.

In addition, when a new page is added to the free space list, a new page is added to a portion other than the beginning of the free space list.

4A to 4C are conceptual views illustrating a method of managing an empty space list using a buffer replacement algorithm according to an exemplary embodiment of the present invention.

Referring to FIG. 4A, first, page 1 200 corresponds to the beginning of an empty space list. Also, page 7 (200) is followed by page 7 (210) by the empty space list.

Referring to FIG. 4B, if a new empty space occurs on page 3, page 3 220 should be added to the empty space list. The added page 3 220 is not inserted at the beginning of the empty space list, but is inserted at another portion. For example, in FIG. 4B, the second page is inserted into the second list.

Referring to FIG. 4C, when new data is inserted, insertion of data occurs at page 1 200, which is the first page in the empty space list. Therefore, recording of data continues until all new data is written to page 1 200 and there is no empty space on page 1 200. In addition, if there is no empty space in the page 1 200 due to the insertion of data, the priority flag of the page 1 200 is set to zero.

Also, the buffer replacement algorithm is about how to set the page on which the empty space is generated on the buffer.

If a new page needs to be allocated to the buffer to record data, first check whether there is room for the new page in the buffer.

If there is space for a new page, the page at the beginning of the free space list is buffered.

In addition, when there is not enough space to put a new page in the buffer, a buffer replacement algorithm is performed to select the victim page.

In the buffer replacement algorithm, pages with a priority flag of 0 are expelled from the buffer. That is, a page with a priority flag of zero is programmed in flash memory, and a new page is allocated to replace the deported page. A page whose priority is flag 0 is not a page in which data is written or a page in which there is no empty space in which data is inserted.

If data is to be inserted into a new page, a new page allocated in place of the deported page is allocated at the beginning of the free space list.

Therefore, when data is inserted into the starting page in the existing empty space list and empty space exists in the starting page, other data may be recorded in the starting page. That is, data recording is performed until there is no empty space in the start page, and when no empty space exists, the priority flag is set to zero.

In particular, as shown in FIG. 4C, in the case of inserting new data into page 1 200, if blank space occurs in page 3 220, page 3 220 is located at the beginning of the free space list. Since it is not inserted, page 1 (200), which is the beginning of the empty space list, allows continuous insertion of data.

In the conventional case, if a blank space occurs in page 3 220, page 3 220 is set as the beginning of the free space list, and insertion of data occurs in page 3 220. Therefore, although there is a blank space in the previous start page, page 1 (200), there is a problem that the new data is no longer written to the page 1 (200), the priority flag is set to 1. However, according to the present invention, the page in which the empty space is generated is inserted in the middle of the list, so that in the page being recorded or to be recorded, continuous data can be recorded until there is no empty space.

Afterwards, the priority flag is set to 0, and pages without empty space are selected as victim pages through a buffer replacement algorithm. Pages with no free space selected as victim pages are written to flash memory through a programming operation. Therefore, the shortening of the life of the flash memory due to the frequent programming operation is prevented as compared with the related art.

In addition, in the present embodiment, the priority flag is distinguished into only two classes, 0 and 1, according to the state of the page into which data is inserted. However, it is possible to vary the criteria for assigning priorities, and to assign several levels of priority according to the criteria. In particular, the buffer replacement algorithm may be applied according to the priority by assigning the highest rank to the root page, which is the top page of each page group, and the next rank of the next higher page.

As described above, when a priority flag is set for each page allocated to the buffer, and a new page is inserted into a list other than the first page in the free space list, a page for recording new data Is not changed, and there is an advantage that the data can be recorded until there is no empty space, and the number of times of programming and subsequent erasing operation of the page occurring every insertion of data can be minimized. Therefore, the deterioration of the life of the flash memory due to frequent erase operations is improved.

1 is a conceptual diagram illustrating a conventional empty space list.

2 is a flowchart for explaining a conventional non-clustering method when there is an insertion of data.

3A to 3F are conceptual views illustrating a process of performing a programming operation through a conventional buffer replacement algorithm.

4A to 4C are conceptual views illustrating a method of managing an empty space list using a buffer replacement algorithm according to an exemplary embodiment of the present invention.

Claims (5)

In the method for managing page-allocated data of flash memory, Setting a priority flag on a page allocated on the buffer; Selecting a victim page by reflecting the priority flag; Programming data written to the victim page into the flash memory and expelling the victim page from the buffer; And Allocating a page of the flash memory to the buffer in a space other than the first page in an empty space list, wherein the first page is performed until there is no space to write data, and is newly allocated to the buffer. And a page has a storage space in which data can be written. The method of claim 1, wherein the priority flag, And a case in which empty space exists in a page on the buffer and a case in which empty space does not exist in a page on the buffer. delete The data management method of claim 1, wherein when the priority flag indicates a page having no empty space, the priority flag is expelled from the empty space list. The method of claim 4, wherein the expulsion from the free space list comprises programming data of a page having no free space into a flash memory.

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