Paweł Lebioda, Tomasz Kapela · 2017-12-14 · Block storage Volatile Memory Persistent Memory...

Paweł Lebioda, Tomasz Kapela

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Agenda

Introduction:

• Persistent Memory

• NVML

• PMEMCHECK

Tutorial:

• Kernel support

• NVML overview

• libpmem

• libpmemblk

• libpmemobj C API

• libpmemobj C++ API

• PMEMCHECK

Just a little bit of theory...

What is it ?

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Persistent Memory

What is Persistent Memory ?

Non-volatile

Retains data without power

Byte addressable

Load/Store access

Memory-like performance

DMA-able

NVDIMM

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Persistent Memory use cases

Block storage

Volatile Memory

Persistent Memory aware filesystem

Persistent Memory aware applications

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Persistent Memory characteristics

Stores are not durable

The data must be flushed

8-byte atomicity

Virtual address may change

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Persistent Memory kernel support

NVDIMM subsystem

DAX (Direct Access)

ndctl – github.com/pmem/ndctl

DAX support in ext2, ext4, xfs

Non-Volatile Memory Libraries

https://github.com/pmem/nvml

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Persistent Memory Programming Model

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NVML introduction

Set of user-space libraries

PMEM-aware applications

Source code on github - github.com/pmem/nvml

BSD license

Web page - pmem.io

Distros (Fedora, openSUSE)

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NVML libraries

Library Description

libvmem Volatile memory allocator

libvmmalloc malloc() replacement using libvmem

libpmem Low-level support for persistence

libpmemlog Append only log structure

libpmemblk Atomic access to memory blocks

libpmemobj Transactional object store

libpmempool Managing library

„In theory, theory and practice are the same. In practice, they are not”

Albert Einstein

How to configure my Linux OS for persistent memory ?

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Kernel support

Kernel config: NVDIMM, DAX

Persistent memory emulation:

– http://pmem.io/2016/02/22/pm-emulation.html

– X86_PMEM_LEGACY

– Memmap=<size>!<offset>

Create filesystem

Mount with DAX

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Persistent Memory configuration

Quick insight into source tree

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NVML overview

Source tree organization

Building

Running tests

Examples

Packages

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NVML packages

Low level persistent memory support

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libpmem examples

How to check if memory is Persistent Memory ?

How to access Persistent Memory ?

Debug library and log messages

How to make memory persistent ?

Running examples under Valgrind pmemcheck

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How to check if memory is Persistent Memory ?

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How to access Persistent Memory ?

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Running pmem_is_pmem example

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libpmem: turning on log messages

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libpmem: pmem_persist - 1

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libpmem: pmem_persist - 2

Persistent Memory aware tool for Valgrind

github.com/pmem/valgrind

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PMEMCHECK

Valgrind tool

Need to build nvml with special flags

Checks correctness of persistent memory usage

Checking data persistence

Support for transactions (libpmemobj)

NVML: make EXTRA_CFLAGS=-DUSE_VALGRIND

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libpmem: valgrind support

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libpmem: pmem_persist + valgrind pmemcheck

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libpmem: pmem_persist - 2

Persistent Memory pools utils

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pmempool: available commands

Persistent Memory resident array of blocks

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Libpmemblk: examples

Pmempool introduction

Creating pmemblk pool with pmempool

Opening pmemblk pool

Reading pool parameters

Reading and writing blocks

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pmempool: create command

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Opening pmemblk pool

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Reading and writing block

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libpmempool: running example

Persistent Memory Transactional Object Store

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libpmemobj

Creating pmemobj pool with pmempool

Opening pmemobj pool

PMEMoid – persistent memory pointer

Root object

Allocations

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Libpmemobj: simple example

Application which stores list of people

Stores first and last name

Constant size array

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Data structures

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Main function

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List of people

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Insert function - 1

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Insert function - 2

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Object’s constructor

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Clear function

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Recovery

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Running example

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Missing persist

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Valgrind pmemcheck

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libpmemobj: type safety macros

PMEMoid as void *

Type safety macros for convenience

No need to track persistent and volatile pointers

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Type safety macros: data structures

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Type safety macros: insert function

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Type safety macros: clear function

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libpmemobj: foreach macros

API for traversing through all objects

Foreach object per type

Useful for recovery actions

Avoids persistent memory leaks

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Foreach type macro

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libpmemobj: atomic lists API

Circular doubly linked list

Atomic operations

sys/queue – like API

Useful for hybrid persistent-volatile data structures

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atomic lists API: data structures

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Atomic lists API: insert function

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Atomic lists: clear function

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Atomic lists API: listing people

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Atomic lists API: recovery

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libpmemobj: transactions

Most generic API

No need for recovery

Convenient macros

Operations:

– Alloc

– Free

– Modify

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Transactions: data structures

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Transactions: insert function

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Transactions: entry initialization

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Transactions: inserting elements

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Transactions: clear function

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Transactions: listing people

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Transactions: valgrind pmemcheck

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Transactions: valgrind pmemcheck

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C++ API

Using language features

Overloading operators

Hiding required operations

Scope transactions

Lambda

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C++ API: main function

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C++ API: list of people class

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C++ API: listing people

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C++ API: insert function

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C++ API: clear function

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C++ API: list entry class

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C++ API: persistent string

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C++ API: valgrind pmemcheck

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C++ API: valgrind pmemcheck - 1

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C++ API: valgrind pmemcheck - 2

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C++ STL

STL allocator concept for libpmemobj

Using STL containers

Need some changes in std libraries

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C++ STL: list of people class

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C++ STL: list entry class