The SNIA NVM Programming Model: Latest Developments and Challenges. Andy Rudoff, Intel Corporation

Transcription

1 The SNIA NVM Programming Model: Latest Developments and Challenges Andy Rudoff, Intel Corporation

2 Programming Model Four meanings (at least) 2

3 Programming Model: SW Interface to HW Core L1 L1 L2 Core L1 L1 L2 L3 Memory Subsystem Memory bus 3

4 Programming Model: SW Interface to HW Core L1 L1 L2 Core L1 L1 L2 L3 Result: Persistent Memory hardware accessed like memory (cache coherent). Described by ACPI on x86. Memory Subsystem Memory bus 4

5 Programming Model: Instruction Set Architecture MOV Core L1 L1 L2 Core L1 L1 L2 L3 CLWB Memory Subsystem persistent domain 5

6 Programming Model: Instruction Set Architecture MOV Core L1 L1 L2 Core L1 L1 L2 L3 Result: Stores flushed from CPU cache, globally-visible Persistent (on x86) CLWB Memory Subsystem persistent domain 6

7 Programming Model: Exposing to s Management UI Management Library Raw Device Access File API File API Load/Store User File System PM-Aware File System MMU Mappings Driver Kernel 7

8 SNIA NVM Programming Model Mgmt. Block File Memory Management UI Management Library Raw Device Access File API File API Load/Store User File System PM-Aware File System MMU Mappings Driver Kernel 8

9 Memory-Mapped Files File API Load/Store User PM-Aware File System MMU Mappings No Page Cache Kernel Result: Direct Access (DAX) 9

10 Programming Model: The Programmer Experience Tools File API Load/Store Language Runtime Libraries PM-Aware File System MMU Mappings Kernel Result: Safer, less error-prone, idiomatic in common languages 10

11 What s Next for the SNIA NVM Programming Model? 11

12 Active Work More details on flushing to persistence Includes flushing to remote persistence Continue to refine the error model Transactions APIs? 12

13 Why is Flushing a Focus? 13

14 Memory-Mapped Files File API Load/Store User Flush msync() PM-Aware File System MMU Mappings FlushViewOfFile() FlushFileBuffers() Kernel 14

15 Memory-Mapped Files File API Load/Store User Flush msync() PM-Aware File System MMU Mappings FlushViewOfFile() FlushFileBuffers() Kernel 30-year-old mechanism: Just as error-prone today as it was 30 years ago 15

16 Memory-Mapped Files File API Load/Store User Flush msync() PM-Aware File System MMU Mappings FlushViewOfFile() FlushFileBuffers() Kernel 30-year-old mechanism: Just as error-prone today as it was 30 years ago Not Atomic 16

17 Java PersistentSortedMap PersistentSortedMap employees = new PersistentSortedMap(); employees.put(id, data); No flush calls. Transactional. Java library handles it all. See pilot project at: 17

18 What Lies Between: Memory-Mapped Files Flush msync() FlushViewOfFile() FlushFileBuffers() High-Level Language Support PersistentSortedMap employees.put(id, data); 18

19 NVM Libraries: pmem.io C/C++ on Linux and Windows User File API Load/Store NVM Libraries PM-Aware File System MMU Mappings Kernel Open Source libpmem libpmemobj libpmemblk Transactional libpmemlog libvmem 19

20 Types of Store Barriers Barrier Type API Optimized Flush Remote Flush Deep Flush Fully specified Fully supported: Linux (ext4, XFS) Windows (NTFS) Current Status Specified, but evolving (ask when safe) Linux: unsafe except Device DAX (and new file systems) Windows: safe Proposals under discussion (works today with extra round trip) Upcoming Specification Transactions Built on above via libraries and languages Much more language support to do 20

21 Summary SNIA NVM Programming Model Both Windows and Linux support basic model Evolving to meet ongoing needs of community Interesting work ongoing on remote PM Expect specs this year in SNIA & other forums Continued refinement of the SNIA model in TWG Flush semantics Error semantics Transactions, and more Ongoing community work on libraries & languages