Access-based eviction of blocks from solid state drive cache memory

Patent metadata

Field	Value
Publication number	US-2016239222-A1
Application number	US-201514623731-A
Country	US
Kind code	A1
Filing date	Feb 17, 2015
Priority date	Feb 17, 2015
Publication date	Aug 18, 2016
Grant date	—

Abstract

Methods and systems are presented for allocating CPU cycles among processes in a storage system. One method includes operations for maintaining segments in a first memory, each segment including blocks, and for maintaining a block temperature for each block in a second memory. The first memory is a read-cache where one segment is written at a time, and each block is readable from the first memory without reading the corresponding complete segment. The block temperature is based on the frequency of access to the respective block, and a segment temperature is based on the block temperature of its blocks. Additionally, the segment with the lowest segment temperature is selected for eviction from the second memory, and blocks in the selected segment with a block temperature greater than a threshold temperature are identified. The selected segment is evicted, and a segment with the identified blocks is written to the first memory.

First claim

What is claimed is:

1 . A method comprising:
maintaining, in a first memory, a plurality of segments, each segment including a plurality of blocks, and maintaining, in a second memory, a block temperature for each of a plurality of blocks, wherein the first memory is a read-cache memory where one segment is written at a time, wherein each block is readable from the first memory without reading the corresponding complete segment, each block temperature being based on a frequency of access to the respective block, wherein a segment temperature for each segment is based on the block temperature for the corresponding plurality of blocks within the segment; selecting a segment from a plurality of segments with a lowest segment temperature for eviction from the second memory; identifying blocks in the selected segment with a block temperature greater than a threshold temperature; evicting the selected segment from the first memory; and writing to the first memory a new segment having the identified blocks, wherein writing to the first memory further includes,
storing blocks in a third memory;
creating the new segment with the identified blocks and additional blocks until the segment is full;
storing in a single operation the new segment in the first memory; and
maintaining the temperature of the identified blocks and initializing the temperature of blocks first cached in the first memory.

2 . The method as recited in claim 1 , wherein the block temperature increases when the block is accessed, wherein the block temperature decreases periodically.

3 . The method as recited in claim 1 , wherein the segment temperature is equal to a total number of bytes in blocks with temperatures greater than or equal to a temperature threshold.

4 . The method as recited in claim 1 , wherein the first memory is a solid-state drive (SSD).

5 . The method as recited in claim 1 , wherein the second memory is one of a random access memory (RAM) or a dynamic random-access memory (DRAM).

6 . A method comprising:
maintaining, in a first memory, a plurality of segments, each segment including a plurality of blocks, and maintaining, in a second memory, a block temperature for each of a plurality of blocks, wherein the first memory is a read-cache memory where one segment is written at a time, wherein each block is readable from the first memory without reading the corresponding complete segment, each block temperature being based on a frequency of access to the respective block, wherein a segment temperature for each segment is based on the block temperature for the corresponding plurality of blocks within the segment; selecting a segment from a plurality of segments with a lowest segment temperature for eviction from the second memory; identifying blocks in the selected segment with a block temperature greater than a threshold temperature; evicting the selected segment from the first memory; and writing to the first memory a new segment having the identified blocks; wherein each block is associated with a volume, wherein each segment is operable to include blocks from one volume and each segment is operable to include blocks from a plurality of volumes; wherein each block has a first block address defined by a corresponding volume and an offset within the volume, the method further including: translating the first block address to a second block address defined by a segment where the block is stored and an offset within the segment; and identifying an ordinal of the block within the segment based on the offset of the second block address.

7 . (canceled)

8 . A method comprising:
maintaining, in a first memory, a plurality of segments, each segment including a plurality of blocks, and maintaining, in a second memory, a block temperature for each of a plurality of blocks, wherein the first memory is a read-cache memory where one segment is written at a time, wherein each block is readable from the first memory without reading the corresponding complete segment, each block temperature being based on a frequency of access to the respective block, wherein a segment temperature for each segment is based on the block temperature for the corresponding plurality of blocks within the segment; selecting a segment from a plurality of segments with a lowest segment temperature for eviction from the second memory; identifying blocks in the selected segment with a block temperature greater than a threshold temperature; evicting the selected segment from the first memory; writing to the first memory a new segment having the identified blocks; and identifying a second plurality of segments whose block temperature is not maintained for the blocks in the segments, wherein the segment temperature for the second plurality of segments is equal to a number of active bytes in the segment.

9 . The method as recited in claim 1 , wherein a read-cache memory is a memory acting as a cache for read requests and not acting as a cache for write requests.

10 . (canceled)

11 . The method as recited in claim 1 , wherein the identified blocks are copied forward by being re-cached in the first memory, wherein blocks in the segment that were not identified are not copied forward.

12 . A method comprising:
maintaining, in a first memory, a plurality of segments, each segment including a plurality of blocks, and maintaining, in a second memory, a block temperature for each of a plurality of blocks, wherein the first memory is a read-cache memory where one segment is written at a time, wherein each block is readable from the first memory without reading the corresponding complete segment, each block temperature being based on a frequency of access to the respective block, wherein a segment temperature for each segment is based on the block temperature for the corresponding plurality of blocks within the segment; selecting a segment from a plurality of segments with a lowest segment temperature for eviction from the second memory; identifying blocks in the selected segment with a block temperature greater than a threshold temperature; evicting the selected segment from the first memory; writing to the first memory a new segment having the identified blocks; and identifying a third plurality of segments utilizing a first in first out (FIFO) process for being cached in the first memory, wherein the segment temperature for the third plurality of segments is equal to a predetermined fixed value.

13 . The method as recited in claim 1 , wherein selecting a segment further includes:
calculating the segment temperature for segments cached in the first memory; and selecting the segment with the lowest calculated temperature.

14 . The method as recited in claim 1 , wherein a non-volatile random-access memory (NVRAM) memory is used as write cache, wherein the segments are formed in the NVRAM and transferred to hard disk storage.

15 . A system comprising:
a first memory for storing a plurality of segments, each segment including a plurality of blocks, wherein the first memory is a read-cache memory where one segment is written at a time, wherein each block is readable from the first memory without reading the corresponding complete segment; a second memory for storing a block temperature for each of the plurality of blocks, each block temperature being based on a frequency of access to the respective block, wherein a segment temperature for each segment is based on the block temperature for the corresponding plurality of blocks within the segment; and a processor operable to select a segment from a plurality of segments with a lowest s

Assignees

• Nimble Storage Inc

Inventors

• Shetty Pradeep
• Karmarkar Sandeep
• Ramamoorthy Senthil Kumar
• Maheshwari Umesh
• Buca Vanco

Classifications

• G06F3/061

  Improving I/O performance · CPC title

• G06F12/128

  adapted to multidimensional cache systems, e.g. set-associative, multicache, multiset or multilevel · CPC title

• G06F3/0617

  in relation to availability · CPC title

• G06F3/0665

  at area level, e.g. provisioning of virtual or logical volumes · CPC title

• G11C7/1072

  for memories with random access ports synchronised on clock signal pulse trains, e.g. synchronous memories, self timed memories · CPC title