Two-level system main memory
Embodiments of the invention describe a system main memory comprising two levels of memory that include cached subsets of system disk level storage. This main memory includes “near memory” comprising memory made of volatile memory, and “far memory” comprising volatile or nonvolatile memory storage that is larger and slower than the near memory. The far memory is presented as “main memory” to the host OS while the near memory is a cache for the far memory that is transparent to the OS, thus appearing to the OS the same as prior art main memory solutions. The management of the two-level memory may be done by a combination of logic and modules executed via the host CPU. Near memory may be coupled to the host system CPU via high bandwidth, low latency means for efficient processing. Far memory may be coupled to the CPU via low bandwidth, high latency means.
1. A system comprising:
system main memory, the system main memory including a first memory level of volatile memory and a second memory level comprising a non-volatile memory, the first memory level being a near memory comprising one or more Dynamic Random Access Memory (DRAM) devices, the first memory level to include a cached subset of the second memory level, the second memory level being larger and slower in comparison with the first memory level, wherein the system main memory is to be communicatively coupled to a processor that is separate from the system main memory, and wherein a size of the system main memory to be presented to an operating system (OS) comprises an available size of the second memory level; and
a two-level memory (2LM) controller to transfer data between the second memory level and the first memory level of the system main memory and the processor based on one or more OS requests, the 2LM controller to direct requests whose targeted data segments are stored within the first memory level to the first memory level, the 2LM controller to direct requests whose targeted data segments are not stored in the first memory level to a far memory controller that controls the second memory level, the 2LM controller comprising a tag table to identify which stored data segments are stored in the first memory level.
2. The system of claim 1 , further comprising: disk storage memory.
3. The system of claim 2 , wherein the second memory level is to include a cached subset of the disk storage memory.
4. The system of claim 2 , wherein the second memory level and the disk storage memory are included in a memory subsystem comprising at least one nonvolatile memory device, and control logic, and:
the far memory controller is to partition the memory subsystem into two or more partitions including a memory partition comprising the second memory level and a disk storage memory partition.
5. The system of claim 4 , wherein the at least one nonvolatile memory device of the memory subsystem is included in a solid state drive (SSD).
6. The system of claim 1 , wherein the non-volatile memory of the second memory level comprises phase change memory.
7. The system of claim 1 , wherein the 2LM controller is included in the processor.
8. The system of claim 1 , wherein the 2LM controller, in response to a detected uncorrectable error in a data segment included in the first memory level, is to further:
determine if the data segment is unmodified with respect to a corresponding data segment included in the second memory level;
copy the corresponding data segment included in the second memory level to the first memory level in response to a determination that the data segment is unmodified; and
report a system error if the data segment is modified.
9. The system of claim 8 , wherein the 2LM controller, in response to a detected uncorrectable error in the corresponding data segment included in the second memory level, is to further report a system error.
10. The system of claim 1 , wherein the first memory level is coupled with the processor by a first means and the second memory level is coupled with the processor by a second means, the first means having higher bandwidth and lower latency in comparison with the second means.
11. The system of claim 1 , wherein the OS and system applications are unaware of the first memory level.
12. The system of claim 1 , wherein the near memory is a transparent cache of the second memory level.
13. The system of claim 1 , further comprising:
a near memory controller to manage near memory.
14. The system of claim 1 , wherein the 2LM controller is to fetch a data segment from second memory level and to write the data segment to near memory upon a determination that the data segment is not in near memory.
15. A two-level memory (2LM) controller implemented on a semiconductor chip, comprising:
first hardware logic circuitry to determine if a data operand of a request received from a processor is stored in a first memory level of a main memory, wherein the first memory level of the main memory is to comprise one or more Dynamic Random Access Memory (DRAM) devices and is to include a cached subset of a second memory level of the main memory, the first memory level being a near memory and the second memory level being a far memory that is larger and slower in comparison with the near memory; and
second hardware logic circuitry to retrieve the data operand from the second memory level of the main memory through a far memory controller, the second memory level comprising a non-volatile memory, in response to a determination that the requested data operand is not stored in the first memory level of the main memory.
16. The 2LM controller of claim 15 , further comprising:
third hardware logic circuitry to write the retrieved data operand from the second memory level of the main memory to the first memory level of the main memory.
17. The 2LM controller of claim 15 , wherein the 2LM controller is included in a processor package including the processor.
18. The 2LM controller of claim 15 , further comprising:
fourth hardware logic circuitry to report a system error in response to a detected uncorrectable error in a data segment included in the second memory level of the main memory.