Tag Archives: Persistent Memory

It’s been more than a year since I last posted; it’s not that I haven’t been busy, but rather that I’ve been trying to do too many things and have been (more slowly than I’d like) cutting back on some of my activities.

Still, I miss using this as a (one way) discussion about my own work. In the past year I’ve managed to publish one new (short) paper, though the amount of work that I put into it was substantial (it was just published in Computer Architecture Letters). This short article (letter) journal normally provides at most one revise and resubmit opportunity, but they gave me two such opportunities, then accepted the paper, albeit begrudgingly over the objections of Reviewer # 2 (who agreed to accept it, but didn’t change their comments).

Despite the lack of clear publications to demonstrate forward progress, I’ve been working on a couple of projects to push them along. Both were presented, in some form, at Eurosys as posters.

Since I got back from a three month stint at Microsoft Research (in the UK) I’ve been working on one of those, evolving the idea of kernel bypasses and really analyzing why we keep doing these things; this time through the lens of building user mode file systems. I really should write more about it, since that’s on the drawing board for submission this fall.

The second idea is one that stemmed from my attendance at SOSP 2019. There were three papers that spoke directly to file systems:

• File Systems Unfit as Distributed Storage Backends
• Performance and Protection in the ZoFS User-space NVM File System
• SplitFS: Reducing Software Overhead in File Systems for Persistent Memory

Each of these had important insights into the crossover between file systems and persistent memory. One of the struggles I had with that short paper was explaining to people “why file systems are necessary for using persistent memory”. I was still able to capture some of what I’d learned, but a fair bit of it was sacrificed to adding background information.

One key observation was around the size of memory pages and their impact on performance; it convinced me that we’d benefit from using ever larger page sizes for PMEM. Some of this is because persistent memory is, well, persistent and thus we don’t need to “load the contents from storage”. Instead, it is storage. So, we’re off testing out some ideas in this area to see if we can contribute some additional insight.

The other area – the one that I have been ignoring too long – is the thesis of this PhD work in the first place. Part of the challenge is to reduce the problem down to something that is tractable and can be finished in a reasonable amount of time.

One of the questions (and the one I wanted to explore when I started writing this) is a rather famous article from 1945 entitled As We May Think. Vannevar Bush described something quite understandable, yet we have not achieve this, though we have been trying – one could argue that hypertext stems from these ideas, but I would argue that hypertext links are a pale imitation of the rich assistive model Bush lays out when he describes the Memex.

Thus, to the question, which I will reserve for another day: why have we not achieved this yet? What prevents us from having this, or something better, and how can I move us towards this goal?

I suspect, but am not certain, that one culprit may be the fact we decided to stick with an existing and well-understood model of organization: