source: Arthur Sainio, In-memory computing summit,2016

NVMW’16
SNIA NVM Summit
IMW
DATE
MEMSYS

Steps:

1. Download the NVDIMM Kernel Tree
2. Compile kernel with the following configurations to enable PMEM and DAX support.
   • CONFIG_BLK_DEV_RAM_DAX=y
     CONFIG_FS_DAX=y
     CONFIG_X86_PMEM_LEGACY=y
     CONFIG_LIBNVDIMM=y
     CONFIG_BLK_DEV_PMEM=m
     CONFIG_ARCH_HAS_PMEM_API=y
3. If you have NVDIMMs, then you should have kernel support. If you don’t have NVDIMMs, you can still test the new PMEM features via volatile memory (i.e. DRAM ) mapping.
4. Volatile memory mapping
   1. check your dmsg and find the usable memory range:
      1. 
      2. You can see physical memory after 0x00000001000000000 (4G) is useable.
   2. Set the kernel parameter in the GRUB memmap=16G!4G. You will reserve a 12GB physical memory  after 4G address , and Linux will treat this memory as a PMEM.
   3. Reboot
5. Check if you have pmem device
   1. ls /dev/pmem0
   2. fdisk -l /dev/pmem0Disk /dev/pmem0: 16 GiB, 17179869184 bytes, 33554432 sectors
      Units: sectors of 1 * 512 = 512 bytes
      Sector size (logical/physical): 512 bytes / 512 bytes
      I/O size (minimum/optimal): 512 bytes / 512 bytes
6. Format ext4 file system and mount
   1.  mkdir /mnt/pmem
   2. mkfs.ext4 -F -b 4096 /dev/pmem0
   3. mount -o dax /dev/pmem0 /mnt/pmem

Links:

NVDIMM Kernel Tree: https://git.kernel.org/cgit/linux/kernel/git/nvdimm/nvdimm.git

NDCTL: https://github.com/pmem/ndctl.git

ACPI 6: http://www.uefi.org/sites/default/files/resources/ACPI_6.0.pdf

NVDIMM Namespace: http://pmem.io/documents/NVDIMM_Namespace_Spec.pdf

DSM Interface Example: http://pmem.io/documents/NVDIMM_DSM_Interface_Example.pdf

Driver Writer’s Guide: http://pmem.io/documents/NVDIMM_Driver_Writers_Guide.pdf

Non-volatile memory ( NVM ) is a type of computer memories that can retrieve stored information across even power failure. Unlike volatile memory, NVM does not need its memorized data to be refreshed periodically. It is commonly used for secondary storage or long-term consistent storage.  Examples of mechanical NVMs storage include, hard disk drive (HDD) and magnetic tape. Another type of NVMs is electrical. Examples of electrical NVM storage include, EEPROM,  Flash memory, and solid-state drive (NAND flash SSD)

Recent in developing NVM technologies include:

• 3D XPoint(Intel, Micron)
• ReRAM(CrossBar)
• Memristor (HP, SK Hynix)
• Nano-RAM (Nantero)
• Phase Change Memory (Intel, Micron, IBM)
• STT-RAM
• Race Track

To make memory persistent, we are facing a number of challenges:

1. How to ensure information stored is durable? The computer system still includes volatile cache memory system. We need to ensure data in caches is flushed. When and how to flush the data impact the system performance .

2. How to ensure consistency of updates? Modern computer have multiple layer private and shared caches.  One data could have multiple copies in caches. How to ensure consistency is still a big challenge. This requires change of hardware and software programming models to achieve this goal.