Conference

IEEE TCE’06

Authors

Heeseung Jo, Jeong-Uk Kang, Seon-Yeong Park, Jin-Soo Kim, Joonwon Lee

Summary

Motivation

LRU policy is not appropriate buffer management policy for a typical file access pattern for PMP.

The policy that is well aware of the characteristics of NAND flash memory and the mechanism of flash controller is needed.

Flash-aware buffer management

LRU is the most common policy for selecting a victim. The characteristices of NAND flash memory prohibits LRU from being the best solution.

FAB is designed to achieve the following purposes:

  • minimize the number of write and erase operations in flash memory
  • the mechanism should help the storage controller to utilize the wsitch merge
  • maximize overwrite of hot pages
  • minimize the search time to find the requested data in the buffer

If the buffer is full, FAB selects a block as a victim and then flushes all of the pages that belong to the selected block. The victim block is a block that has the maximum number of pages in the buffer. FAB also employs a block-level LRU policy.

Most PMP data are contiguous multimedia, most flash memory blocks are either full of valid pages or empty.

However, the blocks for file metadata are very probable that only several pages are updated frequently and some valid and invalid pages are mixed together.

Three major advantages of FAB:

  • Reduced write and erase operations

    FAB allows flushing the pages that belong to the same block at once when the block is replaced.

  • Response time

    Writing multimedia data on the buffer rather than on flash memory will reduce response time significantly

  • Hot page filtering

    In FAB, hot pages are serviced in the buffer.

FAB selects a victim block by the following rules:

  • The block which has the largest number of pages is selected
  • If multiple blocks are selected by the above rule because all of them have the same number of pages in the buffer, then the block at the tail of the list(LRU) is selected.