FlatFlash: Exploiting the Byte-Accessibility of SSDs Within A Unified Memory-Storage Hierarchy

Ahmed Abulila1, Vikram Sharma Mailthody1, Zaid Qureshi2, Jian Huang1, Nam Sung Kim1, Jinjun Xiong3, Wen-mei Hwu 11 ECE, 2 CS, University of Illinois at Urbana-Champaign, Urbana, IL 61801

3 Cognitive Computing & University Partnership, IBM Thomas J. Watson Research Center, Yorktown Heights, NY 10598

Storage Session: 11:30 AM on Wednesday 17th April 2019

mmap()munmap()msync()

File

Virtual MemoryApplication File System SSD

OS

File System

Application

SSD

Virtual MemoryStalls the process

DRAM thrashing/pollution

High I/O Tra c

Page-level persistency

BlockInterface

DRAM in SSD PCIe MMIO Cache Coherence

Page Promotion to Host DRAM

Off-Critical Path Page Promotion

In-Flight Promotion with Cache-Line Granularity

Set Bits in Promotion Look-aside Buffer

Handle Data Access Conflict

CacheHost Bridge

Promotion Lookaside Buffer

SSD

SSD-CacheCPU

flush cache lines:clflush/clwb

verify addr & disable promotion

PCIe

write-verify read❶

❷

❸

FlatFlash disables page promotion for persistent memory regions

create_pmem_region (void* vaddr, size_t size)

Scalable Logging for Database

SSD

Centralized Log Buffer

TXA

TXB

TXC

LockContention

SSD

Log Log Log

TXA TXB TXC

(a) Logging with block I/O (b) Logging with FlatFlash

Metadata Durability in File Systems

root

pointer block

pointer block

inodes

data block

met

adat

a stru

ctur

e

packed in blocks

Put It All Together

Byte-accessibility with PCIe MMIO + OpenCAPI

Unified Memory Space

Adaptive Page Promotion

Byte-Granular Data Persistency

Paper Download

Results

Ensuring Data-Consistency During Page Promotion

Enabling Byte-Granular Data Persistence

System Implications of FlatFlash

Using Flash as Non-Volatile Memory

Limitations of Block I/O Interface

Enabling the Byte-Accessibility of SSDs

Unifying the Memory and Storage

Performance Challenges