> For the complete documentation index, see [llms.txt](https://sliu583.gitbook.io/blog/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://sliu583.gitbook.io/blog/conference/index/sosp-21/nvm/hemem-scalable-tiered-memory-management-for-big-data-applications-and-real-nvm.md).

# HeMem: Scalable Tiered Memory Management for Big Data Applications and Real NVM

### Presentation 

* DRAM + NVM tiered memory 
  * NVM: 8x capacity, 2x latency, assymetric read/write bandwidth, high overhead for small accesses 
* Hardware tiered memory 
  * Example: Intel Optane Memory mode
    * no OS support needed
    * low overhead
    * no visibility into apps
    * limited to simple management techniques 
* Software tiered memory 
  * Insights into applications, support complex policies 
  * But
    * Does not scale to NVM capacity (due to page table overheads)
    * No support for asymmetric read / write bandwidth 
    * Limited flexibility 
* HeMem design principles 
  * Asynchronous memory access sampling with CPU performance counters
    * PEBS memory access sampling 
  * Asynchronous memory migration with DMA offload 
    * Hot/code classification 
    * Mark the pages as WP 
    * DMA copy memory in the background 
  * Data scalability awareness 
  * Focus on asymmetric NVM bandwidth
  * Flexibility