Accelerating garbage collection of flushed logical erase blocks in non-volatile memory

Abstract

A controller of a non-volatile memory tracks identifiers of logical erase blocks (LEBs) for which programming has closed. A first subset of the closed LEBs tracks LEBs that are ineligible for selection for garbage collection, and a second subset of the closed LEBs tracks LEBs that are eligible for selection for garbage collection. The controller continuously migrates closed LEBs from the first subset to the second subset over time. In response to closing a particular LEB, the controller places an identifier of the particular LEB into one of the first and second subsets selected based on a first amount of dummy data programmed into the closed LEBs tracked in the first subset. Thereafter, in response to selection of the particular LEB for garbage collection, the controller performs garbage collection on the particular LEB.

Description

BACKGROUND OF THE INVENTION[0001]This disclosure relates to data processing and data storage, and more specifically, to garbage collection in a non-volatile memory system. Still more particularly, the disclosure relates to techniques for accelerating garbage collection of flushed logical erase blocks in a non-volatile memory system.[0002]NAND flash memory is an electrically programmable and erasable non-volatile memory technology that stores one or more bits of data per memory cell as a charge on the floating gate of a transistor or a similar charge trap structure. The amount of charge on the floating gate modulates the threshold voltage of the transistor. By applying a proper read voltage and measuring the amount of current, the programmed threshold voltage of the memory cell can be determined and thus the stored information can be detected. Memories storing one, two, three and four bits per cell are respectively referred to in the art as Single Level Cell (SLC), Multi-Level Cell (...

AI Technical Summary

Benefits of technology

[0006]The present application recognizes, however, that mandating a delay in garbage collection for a LEB until it is fully programmed and experiences at least one page invalidation greatly reduces overprovisioning. It also recognizes that any additional delay to prevent garbage collection after experiencing at least one logical page invalidation reduces overprovisioning even further. This effect is particularly pronounced in memory technologies like 3D NAND flash memory, which can require some LEBs to be flushed (i.e., written with dummy data) rather than completed with valid host data in order to mitigate certain cell-to-cell interference characteristics of the memory.

[0007]Accordingly, in various embodiments disclosed herein, garbage collection of flushed LEBs containing dummy data is accelerated. In at least one embodiment, a controller of a non-volatile memory tracks identifiers of logical erase blocks (LEBs) for which programming has closed. A first subset of the closed LEBs tracks LEBs that are ineligible for selection for garbage collection, and a second subset of the closed LEBs tracks LEBs that are eligible for selection for garbage collection. The controller continuously migrates closed LEBs from the first subset to the second subset over time. In response to closing a particular LEB, the controller places an identifier of the particular LEB into one of the first and second subsets selected based on a first amount of dummy data programmed into the closed LEBs tracked in the first subset. Thereafter, in response to selection of the particular LEB for garbage collection, the controller performs garbage collection on the particular LEB.

Problems solved by technology

Further, in prior art systems that use a delay queue pool, LEBs were not eligible for garbage collection after the first logical page invalidation until a certain number of write requests were processed or a certain amount of time elapsed.

The present application recognizes, however, that mandating a delay in garbage collection for a LEB until it is fully programmed and experiences at least one page invalidation greatly reduces overprovisioning.

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