KR20100084722A - A web browser cache management technique for mobile full browsing on nand-based devices - Google Patents

Abstract

PURPOSE: A web browser caching method for a NAND flash memory based system which supports full browsing is provided to selectively store a web page file which the probability of being reused is high and a renewal is not occurred in a web browser cache, thereby improving the performance of the web browser cache and extending the lifetime of a NAND flash memory. CONSTITUTION: If a user requests the access of a web page on a web browser through a mouse or a keyboard, the web browser examines a file saved in a cache(102). If the requested file exists, the web page reads the requested file and is indicated on a screen. If the requested file does not exist, the requested file is received from a web server. If the storage into the cache about the requested file is decided, the file is saved and is outputted through the screen.

Description

A Web Browser Cache Management Technique for Mobile Full Browsing on NAND-based Devices}

The present invention is a web browser cache management technique in a device that uses NAND flash memory as an auxiliary storage device and supports full browsing.

(1) Full Browsing Service

A full browsing service is a service that provides a web page screen to a user, similar to using the Internet on a desktop computer, when using the Internet in an environment in which hardware resources are inferior to a desktop computer such as a mobile phone, a PDA, or a PMP. Say.

       (2) Web browser and web browser cache

A web browser is an application program that interprets a file downloaded from a web server so that a user can view it and outputs it to the screen. When a user requests a web page through a mouse or keyboard on a web browser screen, the web browser requests the file from a web server and temporarily stores the file in a memory space of the user's computer so that the user can read it. If the user later visits the web page again, the downloaded file is stored in the web browser cache to avoid downloading from the web server. In general, the web browser is designed to allow the user to specify the size of the web browser cache, and when files larger than this fixed capacity are to be stored, the most unused files are deleted in a sorted order in the unused order. It works by saving old files.

(3) NAND flash memory

NAND flash memory consists of several blocks, each of which consists of several pages. Each page becomes the basic unit of reading and writing, and each block becomes the basic unit of erasing. NAND flash memory has fast read speeds but very slow write and erase speeds. Also, NAND flash memory does not support update operations. Therefore, updating requires invalidating the existing page area and storing new data in another page. Therefore, where each data is stored, it is stored in the file system or the address translation layer called Flash Tranlation Layer to use when reading or updating data. As the invalidated area increases, the available flash area decreases. Therefore, the invalidated area inside the NAND flash memory must be emptied and used through a delete operation through a garbage collection operation. The garbage collection operation selects a block that stores a large number of invalidated areas, copies the data that is still valid within that block to another new block, and deletes the block that stores a large amount of the invalidated area. NAND flash memory has a limited number of erases per block. That is, if each block is deleted more than the limited number of deletions, when the data is stored in the block, the stability of the data can no longer be guaranteed. Therefore, in order to use NAND flash memory efficiently, each block must be processed to be evenly erased.

When a web browser stores all files downloaded from a web server in a web browser cache, a write request is performed to store the file in NAND flash memory, which is the media of the web browser cache. However, since most web page files are not reusable, storing all of these files in NAND flash memory will use the relatively slow write operations of NAND flash memory. In addition, these files waste read, write, and erase operations during garbage collection operations in flash memory, even when they may be reused. Also, files that are frequently updated cannot be updated in the stored area immediately when they are stored in NAND flash memory, thus increasing the garbage collection load.

As a result, the increased write and erase operations reduce the overall performance of the Web browser cache and shorten the lifetime of the NAND flash memory.

 In the proposed technique, only files related to web pages that are relatively likely to be reused and that update is not likely to be stored are stored in the web browser cache.

In the conventional method, all files downloaded from the web browser are unconditionally written to the NAND flash memory in the web browser cache, causing unnecessary reading, writing, and erasing operations in the NAND flash memory. It causes problems such as a decrease in response time and shortened lifetime of the NAND flash memory.

In this technology, by selectively placing web page files that are relatively likely to be reused and that update is not likely to occur in the web browser cache, the operation of the NAND flash memory such as unnecessary reading, writing, erasing, etc. can be reduced, It can improve performance and extend the life of NAND flash memory.

      (1) Overall operating sequence of the present invention

1 is a flow chart of the technique presented in the present invention. First, when a user requests 101 to access a web page on a web browser via a web page mouse or keyboard, the web browser checks 102 whether there is a file corresponding to a cache. If the requested file exists (103), the requested file is read (104), the user processes the web page (109) and the result is displayed on the screen. If the requested file does not exist (105), the requested file is downloaded from the web server (106). In this case, the proposed technology checks whether to store in the web browser cache (107). If the user decides not to save the file, the file is processed (109) and displayed on the screen, and is not stored in the web browser cache. If it is determined to save (110), after the file is stored (111), after processing the file (109), and outputs the result of the file processing to the user through the screen.

(2) Determine whether to save to web browser cache memory

In 107 of FIG. 1, it is determined whether or not the file requested in the web browser cache is stored in the web browser cache. In order to accomplish this, the present invention records how many files are accessed in the main memory space, and when it is determined that the number of accesses has a predetermined level or more, it stores the data in the NAND flash memory. In addition, NAND flash memory deteriorates even when an update occurs and there is a high possibility that unnecessary operations may occur, thus allowing writing to NAND flash memory only when the number of updates is less than a certain level while the file is stored in main memory. . 2 is a conceptual diagram of a system using a main memory and a NAND flash memory as a web browser. The system has a processor 201 and utilizes the main memory 202 and the NAND flash memory 204 as web browser caches. And communicates with the web server via the network interface 203. Here, when the files are temporarily stored in the main memory 201 and the corresponding files are deleted from the main memory, it is determined whether to store them in the NAND flash memory. The deletion of a file in main memory 201 is determined when the file was read from a web browser. If the user sets the web browser cache value on the main memory 201 in advance, and stores the web page file more than that, the space on the main memory 201 is insufficient. Therefore, the oldest file is used. Will be deleted from).

 At this time, it is determined whether or not to be stored in the NAND flash memory 204 by the flow chart of FIG. FIG. 3 is a flow chart for determining selective storage specifically depicting FIG. 1 107. As described above, when a file is deleted from main memory and arrives at 107, the number of times the file is accessed while in main memory is compared with a threshold value called an access threshold. If the number of accesses of the file is less than the access threshold value, it is determined that it will not be frequently used even if stored in the NAND flash memory (303) and the file is deleted.

In the opposite case 302, how much the file has been updated in main memory is compared with a threshold value called an update threshold. If the file update count is greater than the update threshold (304), it is determined that the file can be updated in the NAND flash memory, and the file is deleted. In the opposite case (305), it is determined that the file is unlikely to be updated in the NAND flash memory and stored in the NAND flash memory.

 Herein, in order to determine an access threshold and an update threshold, the technique of the present invention is determined by referring to the number of files and the number of updates that are deleted without being used in the NAND flash memory.

 As in main memory, NAND flash memory uses the web browser cache only as much as the user-specified size, so when files larger than the specified size need to be stored, the oldest files are deleted. Alternatively, when an update occurs in the NAND flash memory, that is, when an update is required because the file name is the same but the contents are different, the file is deleted in the NAND flash without the update function. Here, deleting means not performing a direct delete operation but invalidating the corresponding part.

 First, if a file is deleted because of its file size, it is checked whether the file has been accessed from the NAND flash memory. If not accessed, this means that the file has never been used since it was stored in NAND flash memory. For convenience, let's call it 'access prediction error'. When invalidation of a file occurs due to the update, the file to be updated is stored in the NAND flash memory. Let's call this 'update prediction error' for convenience.

 FIG. 4 shows how to change the access threshold and the update threshold in consideration of the access prediction error and the update prediction error in the developed technology. This procedure occurs whenever an access prediction error or update prediction error occurs in NAND flash memory. However, in order to prevent the threshold from changing too often, the threshold is not changed until the sum of the access prediction error and the update prediction error reaches a certain level (407).

By doing so, it is possible to dynamically change each threshold for certain prediction errors.

If the number of access prediction errors and update prediction errors occurs as many as a predetermined number (401), it is checked whether the access prediction error has increased compared to the previous or only the access prediction error has continued to occur. If so (402), this means that more files are stored in the NAND flash memory and then not used, meaning that a more stringent access threshold is needed, thus increasing the access threshold. In the opposite case (403) it is determined that many prediction errors are due to update prediction errors rather than access prediction errors, and the current access threshold is reduced. The same check is then made for the update prediction error. If the update prediction error has increased more than before or if only the update prediction error continues (405), it means that many files have been invalidated in NAND flash memory since they have been updated since many files have been stored in NAND flash memory, and therefore a more stringent update threshold. Reduce the update threshold to have In the opposite case (406) increase the update threshold. After that, the current access prediction error and update prediction error value are stored so that they can be used for the next evaluation. The procedure is terminated after initializing to 0 respectively.

1 is a flow chart showing the overall operation of the invention

2 is a conceptual diagram of a system using a main memory and a NAND flash memory as a web browser.

3 is a flow chart for determining selective file storage

4 is a flowchart showing a change in an access threshold and an update threshold.

Claims (9)

How to selectively store files in the web browser cache on devices such as mobile embedded systems or computers that use NAND flash memory as secondary storage and support full browsing The method of claim 1, wherein the access and update records of each file are retrieved from the main memory through temporary storage for a predetermined period for selective file storage. The method according to claim 1, wherein the file access and update records of each file are compared together with the access threshold and the update threshold for selective file storage to selectively store only files whose number of file accesses is greater than the access threshold and the number of updates is less than the update threshold. Way The method of claim 3, wherein the access threshold and the update threshold are dynamically changed according to a user's usage trend. The method of claim 4, wherein the number of files that are never used and invalidated in the NAND flash memory is recorded to change the access threshold, and the access threshold is adjusted according to the increase and decrease trend. The method of claim 4, wherein the number of files updated and invalidated in the NAND flash memory is recorded in order to change the update threshold, and the update threshold is adjusted according to the increase and decrease trend. The method of claim 2, wherein the oldest accessed file is deleted when the main memory is insufficient. The method of claim 4, wherein the oldest accessed file is deleted when the NAND flash memory is insufficient. The method of claim 4, wherein the threshold value is changed at intervals of a predetermined number of events.

Images