Chloe Alverti wrote: > Hi! Hi Chloe,
> > My name is Alverti Chloe and I am a PhD student! I have been > working/studying the past year on system support for persistent > memory. > I wanted to kindly ask you your view about DAX kernel support; will it > continue to evolve/be supported in the mainline since Optane memory > has announced to be over? Short answer, yes, DAX keeps going. Longer answer, just from my perspsective as a Linux kernel developer, not the views of my employer, is that DAX concepts have existed in the kernel since before Intel® Optane™ and will continue to exist after it is gone. Recall that the immediate predecessor to DAX was a facilty called XIP (eXecute In Place), which allowed systems to run binaries direct from byte addressable media without first needing to transfer them to main memory. After DAX arrived, it grew usages outside of persistent memory. Virtual machine hosting environments use it to avoid duplicating page cache inside guests. In those setups a guest accesses a virtual pmem device that the VMM maps to bare metal page cache. Lastly, even without those non-PMEM use cases, it is still the case that all you need is DRAM plus an energy source and flash, and voila you have persistent memory. In general, the term "Storage Class Memory" encompasses a wide range of potential media types. > Is DAX going to be used as an interface for CXL compatible storage devices? At its simplest CXL is just another mechanism for enumerating platform physical address ranges. A facility called 'device-dax' was created to offer dedicated access to "special purpose" / "soft reserved" memory. That facility originated with PMEM, but found usages for other cases where a particular memory was either too slow to be used for general purpose memory allocations (some PMEM technologies), or too precious to be consumed by general purpose allocations (see high-bandwidth-memory). For everything in between there is the ongoing memory-tiering work. However, from my perspective, DAX will continue to play a role in managing dedicated memory access sans page-cache whether it is PMEM or not.
