KR20180076276A - Method for garbage collection of flash memory and storage device using the same - Google Patents

Abstract

The present invention provides a garbage collection method of a flash memory which reduces the number of valid copy operations with respect to a valid page performed whenever deleting a block and can improve input and output performance, and a storage device using the same. According to an embodiment of the present invention, the garbage collection method of a flash memory comprises the following steps of: receiving page cache information which is information about a schedule for changing content of a plurality of pages included in each of a plurality of blocks composing a flash memory, from a host; and selecting a garbage collection target block based on the received page cache information and invalid page information which is information about the page in which the content is invalid among the plurality of pages.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a flash memory and a storage device using the flash memory,

More particularly, the present invention relates to a method and apparatus for selecting a garbage collection target block on the basis of page cache information and invalidation page information, which are schedule change information of a plurality of pages, To a garbage collection method of a flash memory for performing garbage collection, and a storage device using the same.

A flash memory is a nonvolatile memory device that can electrically write data and erase stored data, and the stored information is not erased even when the power supply is cut off.

These flash memories have the advantages of high speed, low power, small size and durability and can be used in mobile phones, digital cameras, PDAs, mobile computer devices, stationary computer devices and other devices.

In flash memory, data read and write operations are performed on a page basis and erase operations are performed on a block basis depending on physical characteristics, and data overwrite operations are not possible. There are disadvantages.

In order to overcome these drawbacks, a flash translation layer is applied to a flash memory to perform additional operations such as logical address mapping, garbage collection, wear leveling, and error correction code Function.

The garbage collection is performed on a block-by-block basis, selects a block to be erased, copies all the valid pages included in the selected block to another block, and erases the selected block And performs an operation.

However, a valid copy operation for a valid page executed every time a block is deleted greatly degrades the overall performance of the flash memory device, such as degradation of memory processing speed and life span.

Therefore, there is a need for a method for reducing the number of valid copy operations for a page (valid page).

A related prior art is Korean Patent No. 10-0789406 entitled " Flash memory system and its garbage collection method, registration date: December 20, 2007. "

According to the present invention, a garbage collection target block is selected based on page cache information and invalidation page information, which are schedule information of a plurality of pages constituting a flash memory, so that data on a valid page Which can improve the input and output performance by reducing the number of valid copy operations, and a storage device using the same.

The problems to be solved by the present invention are not limited to the above-mentioned problem (s), and another problem (s) not mentioned can be clearly understood by those skilled in the art from the following description.

In order to achieve the above object, a garbage collection method of a flash memory provided in the present invention is a method for collecting page cache information which is information on a schedule of contents change of a plurality of pages included in each of a plurality of blocks constituting a flash memory from a host And a step of selecting a garbage collection target block based on the received page cache information and invalid page information, which is information on a page whose content has been invalidated, among the plurality of pages.

The method may further include performing garbage collection on the block to be garbage collected.

Advantageously, the page cache information may be generated from a cache in which the operating system of the host stores information about a change state of the plurality of pages.

Preferably, the step of selecting a block to be garbage collected includes generating predicted page information, which is information on a page on which content change is scheduled among the plurality of pages, from the page cache information, Calculating a garbage collection cost for each of the plurality of blocks on the basis of the number of the predictive pages included in each block and the number of invalidation pages and calculating a garbage collection cost for each of the plurality of blocks based on the calculated cost, And selecting a block.

Advantageously, the step of calculating the cost may further calculate the cost based on a weight for each of the prediction page and the invalidation page.

In order to achieve the above object, a storage device including a controller for selecting a target block for garbage collection provided by the present invention includes a flash memory and a plurality of pages included in each of a plurality of blocks constituting the flash memory from a host A controller that receives page cache information that is information on a content change schedule and selects a block to be garbage collected based on the received page cache information and invalidation page information that is information on a page whose content has been invalidated among the plurality of pages .

Advantageously, the controller is able to perform garbage collection on the garbage collection target block.

Advantageously, the page cache information may be generated from a cache in which the operating system of the host stores information about a change state of the plurality of pages.

Preferably, the controller generates prediction page information, which is information related to a page on which content change is scheduled among the plurality of pages, from the page cache information, and calculates the number of prediction pages included in each of the plurality of blocks, A garbage collection cost for each of the plurality of blocks may be calculated based on the number of revocation pages, and a garbage collection target block may be selected based on the calculated cost for each of the plurality of blocks.

Preferably, the controller may calculate the cost based further on weights for each of the prediction page and the invalidation page.

In order to achieve the above object, the present invention provides a controller for controlling a flash flash memory provided in the present invention, the controller comprising: a memory for storing information about a schedule of contents change of a plurality of pages included in each of a plurality of blocks constituting the flash memory A receiving unit that receives page cache information, and a selection unit that selects a garbage collection target block based on the received page cache information and invalidation page information, which is information on a page whose content is invalid, among the plurality of pages.

According to the present invention, data on a valid page, which is performed each time a block is deleted, is selected by selecting a block to be garbage collected based on page cache information and invalidation page information, which are schedule change information of a plurality of pages constituting a flash memory The input and output performance can be improved by reducing the number of valid copy operations.

FIG. 1 is a flowchart illustrating a garbage collection method of a flash memory according to an embodiment of the present invention. Referring to FIG.
2 is a flowchart illustrating a method of selecting a garbage collection target block according to an embodiment of the present invention.
3 is a block diagram illustrating a storage device including a controller in accordance with an embodiment of the present invention.
4 is a block diagram illustrating a controller for controlling a storage device including a flash memory in accordance with an embodiment of the present invention.
5 is a diagram illustrating a Linux kernel I / O system.
FIG. 6 is a view for explaining a result of selecting a garbage collection target block according to an embodiment of the present invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. Like reference numerals are used for like elements in describing each drawing.

The terms first, second, A, B, etc. may be used to describe various elements, but the elements should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component. And / or < / RTI > includes any combination of a plurality of related listed items or any of a plurality of related listed items.

It is to be understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, . On the other hand, when an element is referred to as being "directly connected" or "directly connected" to another element, it should be understood that there are no other elements in between.

Also, the terms " part, "" unit," " module, "and the like, which are described in the specification, refer to a unit for processing at least one function or operation and may be implemented by hardware or software or a combination of hardware and software .

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the terms "comprises" or "having" and the like are used to specify that there is a feature, a number, a step, an operation, an element, a component or a combination thereof described in the specification, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

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 to which this invention belongs. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the contextual meaning of the related art and are to be interpreted as either ideal or overly formal in the sense of the present application Do not.

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a flowchart illustrating a garbage collection method of a flash memory according to an embodiment of the present invention. Referring to FIG.

Referring to FIG. 1, in step S100, the controller 310 receives page cache information from the host, which is information related to a content change of a plurality of pages included in each of a plurality of blocks constituting a flash memory.

At this time, the page cache information indicates information about a schedule of contents change of a page in which contents are changed in the host but not in the flash memory 320, for a plurality of pages included in each of the plurality of blocks can do.

In step S200, the controller 310 selects a garbage collection target block based on the page cache information and the invalid page information received in step S100.

At this time, the invalidation page means information about a page whose contents are invalid among a plurality of pages.

In another embodiment, the controller 310 may perform garbage collection on the garbage collection target block.

In another embodiment, the page cache information may be generated from a cache in which the operating system of the host stores information on a change state of the plurality of pages.

The method of performing the step S200 will be described in more detail with reference to FIG.

2 is a flowchart illustrating a method of selecting a garbage collection target block according to an embodiment of the present invention.

Referring to FIG. 2, in step S210, the controller 310 generates predicted page information from the page cache information received in step S100.

The predictive page information is generated using page cache information and means information about a page on which a content change is scheduled.

In step S220, the controller 310 calculates a garbage collection cost for each of the plurality of blocks based on the number of the prediction pages included in each of the plurality of blocks and the number of the invalidation pages.

In general, garbage collection selects a garbage collection target block using only the invalidation pages included in a plurality of blocks, and deletes the target block at a certain point in a block unit.

However, in the present invention, the garbage collection target block can be selected using not only the invalidation page but also the prediction page information on which the page content is scheduled to be changed.

In another embodiment, the garbage collection target block is selected based on the garbage collection cost, and the garbage collection cost is calculated using the following Equation (1).

[Equation 1]

Garbage Collection Cost = [Number of Predicted Pages + Number of Invalidated Pages]

That is, in the present invention, the garbage collection cost is calculated by using the sum of the number of predicted pages and the number of revocation pages for a plurality of blocks.

In another embodiment, the controller 310 may calculate the garbage collection cost using the following equation (2) further based on the weights for the prediction page and the invalidation page, respectively.

&Quot; (2) "

Garbage collection cost = [(1-α) * number of predicted pages + α * number of invalidated pages]

Here, a is a constant relating to a weight, and may be a predetermined value for calculating a garbage collection cost.

As described above, by applying a weight to each of the predictive page and the invalidation page to calculate the garbage collection cost, the number of valid copy operations for reading and writing data for a valid page, There is an effect that can be reduced.

In step S230, a garbage collection target block is selected based on the garbage collection cost of each of the plurality of blocks calculated in step S200.

In a preferred embodiment, the controller 310 may select a block having a maximum value among the calculated garbage collection costs for the plurality of blocks as a target block for garbage collection, and perform garbage collection.

Examples of the pseudo code for implementing the method disclosed in FIGS. 1 and 2 are as follows.

Input:
- Number of Free Blocks Number of BLOCK _FREE
- garbage collection execution point ThresholdGC
- Status information of each block (FREE, VALID, INVALID, PREDICTED) BLOKC [i]. Status information
- Predicted page when selecting VICTIM block, INVALID page proper ratio α
- Block to perform current GC BLOCK _{cur _victim}

Output
- Block to perform next GC BLOCK _victim

1. IF (Number of FREE BLOCK <ThresholdGC) THEN
2. BLOCK _cur Perform GC on _{_victim}
3. FOR For all blocks
4. Find (BLOCK [i]. INVALID + BLOCK [i]. PREDICTED) OR of ((1-α) * BLOCK [i]. INVALID + α * BLOCK [i]. PREDICTED) MAX
5. END FOR
6. BLOCKvictim = BLOCK.MAX
7. END IF

At this time, the victim block described in the above table may be a representation of the 'garbage collection target block' described in the present invention.

3 is a block diagram illustrating a storage device including a controller in accordance with an embodiment of the present invention.

Referring to FIG. 3, a storage device 300 including a controller for selecting a block to be garbage collected according to an embodiment of the present invention includes a controller 310 and a flash memory 320.

The host may send a data input / output request to the storage device 300. The data input / output request may include data input / output commands such as write, read, erase, and the like.

In addition, the host may be a personal computer, a server computer, a portable computer including a notebook, a cellular phone, a smart phone, a tablet, MP3, a portable multimedia player (PMP), a personal digital assistant (PDA) Such as a portable device.

The storage device 300 may store data generated when the host performs a predetermined operation. Alternatively, based on the data stored in the storage device 300, the host may perform a preset operation.

In addition, the storage device 300 may include a solid state drive (SSD), a universal flash storage (UFS), and a memory card, and may preferably include an SSD.

The storage device 300 may be configured to store various data processed at the host and may include a cache (not shown). The cache (not shown) generally comprises a DRAM or an SRAM, and may temporarily store read and write data requested by a host.

In the present invention, page cache information, which is information on a change state of a plurality of pages, may be stored in the cache (not shown).

The controller 310 may access the flash memory 320 in response to a host request and may control the read, write, and erase operations on the flash memory 320.

Specifically, when receiving a read request from a host, the controller 310 uses a mapping table for address translation that connects a logical address and a physical address to generate a physical page (logical page number) of a logical page number The physical page number (PPN) information can be read to transfer the data stored in the physical page number to the host.

When the controller 310 receives a write request from the host, the controller 310 processes an invalid page in the block included in the flash memory 320 as an invalid page state, stores new data in a newly allocated page of the new block, The physical page number (PPN) can be modified and recorded in the mapping table.

There are a plurality of blocks in the flash memory 320, and one block is composed of a plurality of pages. Further, the page is divided into a free page, an effective page, and an invalid page.

The free page can be inserted immediately, the valid page is stored with meaningful data, and the invalid page is stored with meaningless data.

The flash memory 320 includes an EEPROM (Electrically Erasable Programmable Read-Only Memory), a Ferroelectrics Random Access Memory (FRAM), a Phase-change Random Access Memory (PRAM), and a Magnetic Random Access Memory Volatile memory device.

The controller 310 receives page cache information from the host, which is information regarding a scheduled content change of a plurality of pages included in each of the plurality of blocks constituting the flash memory (S100).

In operation S200, the controller 310 selects a garbage collection target block based on the received page cache information and the invalidation page information, which is information related to the invalidated page of the plurality of pages.

In another embodiment, the controller 310 may perform garbage collection on the garbage collection target block.

In another embodiment, the page cache information may be generated from a cache in which the operating system of the host stores information about a change state of the plurality of pages.

For example, if the operating system of the host is Linux, the information about the changed state of the page may be stored in the page cache. When a dirty flag indicating whether a page is changed is set in a flag field of a specific page in the page cache, the contents of the specific page where the dirty flag is set are changed in the host, The memory 320 may be a page whose contents have not been changed.

The operating system may generate the page cache information using the dirty flag.

The controller 310 receives the page cache information and generates predicted page information (S210).

In operation S220, the controller 310 calculates a garbage collection cost for each of the plurality of blocks based on the number of the predictive pages included in each of the plurality of blocks and the number of the invalidation pages.

In another embodiment, the controller 310 may calculate the garbage collection cost using Equation (1) described above.

That is, in the present invention, the number of predictive pages and the number of revocation pages are calculated for a plurality of blocks, and a block having a maximum value is selected as a garbage collection target block (S230).

In another embodiment, the controller 310 may calculate the cost using Equation (2) as previously described based further on the weights for the prediction page and the invalid page, respectively.

As described above, the present invention increases the input and output performance by reducing the number of operations of reading and writing data of the validated page performed every time the block is deleted by calculating the cost by further applying weights to the predicted page and the invalidated page, respectively There is an effect that can be made.

4 is a block diagram illustrating a controller for controlling a storage device including a flash memory in accordance with an embodiment of the present invention.

Referring to FIG. 4, a controller 310 of a storage device according to an embodiment of the present invention includes a receiver 312 and a selector 314.

The controller 310 controls the storage device 300 including the flash memory.

The receiving unit 312 receives page cache information from the host, which is information on a content change schedule of a plurality of pages included in each of the plurality of blocks constituting the flash memory.

The selection unit 314 selects a garbage collection target block based on the page cache information received from the receiving unit 312 and the invalidation page information, which is information on the invalidated page of the plurality of pages.

5 is a diagram illustrating a Linux kernel I / O system.

In another embodiment of the present invention, garbage collection can be performed by applying it to an operating system of Linux.

As shown in FIG. 5, the Linux kernel I / O system includes a page cache, a file system, and a block layer (not shown) including a virtual file system (VFS) a general block layer, an I / O scheduler, and a device driver. The Linux kernel I / O system is obvious to those of ordinary skill in the art, so a detailed description thereof will be omitted.

Also, since the kernel I / O system of Linux shown in Fig. 5 is also a host system, it is applicable to the present invention.

That is, in the present invention, the page cache information, which is information on the change status of a plurality of pages, may be stored in the SDRAM in the SSD shown in FIG.

The controller 310 of the present invention can receive the page cache information stored in the SDRAM and generate prediction page information using the page cache information. The controller 310 calculates a garbage collection cost based on the generated predicted page information and the invalidation page information, and performs garbage collection based on the calculated garbage collection cost.

In addition, the present invention can be applied to various operating systems as well as the Linux operating system described above to perform garbage collection.

FIG. 6 is a view for explaining a result of selecting a garbage collection target block according to an embodiment of the present invention.

6 shows a result of selecting a target block for garbage collection using a conventional greedy policy and a target block using a garbage collection target block selection method of the present invention on the right side .

Conventionally, the garbage collection block selection method using the greedy policy is selected as the garbage collection target block using only the invalidation page information. Therefore, since the number of the invalidation pages included in the B block among the A, B, C, and D blocks is the largest, the result of selecting the B block as the target block to be garbage collected is shown.

However, in the present invention, the garbage collection target block is selected based on the invalidation page and the prediction page information.

In a preferred embodiment of the present invention, a block having a maximum value of the sum of the number of revocation pages and the number of predicted pages may be selected as a garbage collection target block. As a result, the block having the maximum value of the sum of the number of the predicted page and the invalidation page becomes the C block. Therefore, C block is selected as the target block for garbage collection, and garbage collection is performed on the selected block.

In another embodiment of the present invention, the garbage collection cost may be calculated based on the weight of each of the invalidation pages and the number of predicted pages to select the garbage collection target block.

As shown in FIG. 6, when a garbage collection target block is selected using a conventional greedy policy, an unnecessary validated page copy operation must be performed.

However, according to the present invention, by using the predictive page information which is the information about the page on which the content change is scheduled, it is possible to reduce unnecessary validated page copying operation, thereby enabling the garbage collection to be performed more efficiently .

The above-described embodiments of the present invention can be embodied in a general-purpose digital computer that can be embodied as a program that can be executed by a computer and operates the program using a computer-readable recording medium.

The computer readable recording medium includes a magnetic storage medium (e.g., ROM, floppy disk, hard disk, etc.), optical reading medium (e.g., CD ROM, DVD, etc.).

The present invention has been described with reference to the preferred embodiments. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. The scope of the present invention is defined by the appended claims rather than by the foregoing description, and all differences within the scope of equivalents thereof should be construed as being included in the present invention.

300: storage device
310: controller
312:
314: Preceding Government.
320: flash memory

Claims (11)

Comprising: receiving page cache information from a host, the page cache information being information concerning a schedule of contents change of a plurality of pages included in each of a plurality of blocks constituting a flash memory; And
And selecting a garbage collection target block based on the received page cache information and invalid page information, which is information about a page whose contents are invalidated among the plurality of pages. The method according to claim 1,
And performing garbage collection on the block to be garbage collected. The method according to claim 1,
The page cache information includes:
Wherein the operating system of the host is generated from a cache storing information on a change state of the plurality of pages. The method according to claim 1,
Wherein the step of selecting a block to be garbage-
Generating predicted page information that is information on a page on which content change is scheduled among the plurality of pages from the page cache information;
Calculating a garbage collection cost for each of the plurality of blocks based on the number of the predictive pages included in each of the plurality of blocks and the number of the invalidation pages; And
And selecting a garbage collection target block based on the calculated cost for each of the plurality of blocks. 5. The method of claim 4,
The step of calculating the cost includes:
Wherein the cost is calculated based on a weight for each of the prediction page and the invalidation page. Flash memory; And
The page cache information being information about a schedule of contents change of a plurality of pages included in each of a plurality of blocks constituting the flash memory from the host, and receiving the page cache information and the contents of the plurality of pages And a controller for selecting a garbage collection target block based on the invalidation page information. The method according to claim 6,
The controller
And performs garbage collection on the block to be garbage collected. The method according to claim 6,
The page cache information
Wherein the operating system of the host is generated from a cache storing information on a change status of the plurality of pages. The method according to claim 6,
The controller comprising:
Generating prediction page information that is information on a page on which content change is scheduled among the plurality of pages from the page cache information based on the number of the prediction pages included in each of the plurality of blocks and the number of invalidation pages And a garbage collection cost for each of the plurality of blocks is calculated and a garbage collection target block is selected based on the cost calculated for each of the plurality of blocks. 10. The method of claim 9,
The controller
Wherein the cost is calculated based further on weights for each of the prediction page and the invalidation page. A controller for controlling a flash memory,
A receiving unit for receiving page cache information from the host, the page cache information being information regarding a schedule of contents change of a plurality of pages included in each of a plurality of blocks constituting the flash memory; And
And a selection unit configured to select a garbage collection target block based on the received page cache information and the invalidation page information, which is information related to a page whose content has been invalidated among the plurality of pages.

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