You are right, if you are directly modifying the mmaped region. I always internally model my data as staging my changes to be synchronized to the mmaped region, so thats my mistake there.
> the page is either unwritable or CoW.
This is not universally true, or maybe I'm confused on this statement. MAP_SHARED exists, but maybe you are referencing a specific kernels' implementation on how they achieve coherence between file backed shared memory regions in two processes? Im not sure.
> Darwin kernel does though.
Sure we can always point to a kernel that has has implemented some feature or another, which is why I said typically you don't see it.
I may have parsed your statement incorrectly, but I'm assuming you are talking about the copy of data when using either mmap or File IO (memcpy versus write) Whether you do File IO versus mmap, there's going to be copy. With files, the copy occurs within kernel space with data being copied into the pages in the buffer cache, with mmap the copy occurs in userspace with data being copied into the address space. Swapping can occur in the buffer cache or mmap, this is why so many databases implement their own buffer cache to ensure specific data isn't flushed, leaving them in an inconsistent state.
I can understand these folks struggling with what mmap is actually doing. But this isn't a new discussion about the qualities of MMAP versus file based IO etc. Although, many of the comments stated are quite wrong.
I'm going to self plug here on work I'm apart of that does persistent processes, although the motivation is different. I do think this paper does a good job of informing the reader on why these sort of features would be really cool that this project does not necessarily dive into. But it requires widening the API and allowing for developers to choose how they persist.
Many conferences are starting to adopt a badge system and will evaluate your artifact. And this is becoming more and more popular, and I know many researchers that will keep these badges in mind when reading the evaluation in the paper. For example here is the artifact evaluation that was done at SOSP 2021 https://sysartifacts.github.io/sosp2021/results.html.
Its unfortunate with teaching as I see it as an opportunity to extend the good values of research and problem solving to students (at least in the later years of a degree).
I guess it depends on how you view an academic institution, is it to produce good thinkers or produce good work, although similar seems like you approach it in different ways when approaching it from one way or the other.
I'm not even upset with professors, I think Assistant Profs do the most work I've ever seen anyone ever do, its absolutely insane the crazy workload they take on to get tenure.
Professors are rewarded for publications and almost nothing else (at least from what I've seen at the school I'm apart of), so because of it all effort goes towards publications, and this passes down to students and the folks they hope to hire. Its also unfortunate any work that is not done towards a publication is essentially invisible to everyone within that system. Even things like teaching are considered second class to publications (very unfortunate consequence).
That being said this is from my experience and am unsure how it is at other schools.
Counts what you are afraid against. There's always some side channel attack that could possibly used to gain information, even on VM's this is true. Off the top of my head there could be some timing attack to gain information on which libraries others are using by reading in libraries and seeing if they are warm in the buffer cache, counts if you care about sharing the same kernel. I generally find them secure enough considering how fast they can be brought up and down.
I think you are assuming all these things are independent of one another. I think deep engagement with customers directs your problem statement. Build the smallest possible thing to test the idea you are proposing. If you are trying to publish than its a requirement to be reading papers in general, you need to be able to argue why this idea you are testing is orthogonal to other ideas being proposed. As time goes on you just scan important conferences in your field and get better at knowing which papers you need to skim versus deeply understand.
Edit: Also intelligence is an over-rated metric, persistence is far more important when it comes to these hard problems.
This seems to be a solution that comes at the cost of the consumer which is fine if they want to pay for it, and seems to be an option provided for more latency sensitive applications.
Obviously, one could eliminate the cold start issue in general by just constantly paying for a running EC2 instance.
But cold start is still an issue for the provider as cold start is a cost to them, even reducing cold start of internal runtimes would be a massive benefit (For example pre-warmed JITs). Better cold start times means better bin packing for their services, and overall less cost to everyone.
Lots of interesting work is being done in this area (Currently doing research around serverless at the moment). Cold start up times still remain a pretty large issue (125ms start up for VM is still quite large) but some interesting papers trying to attack this, through strategies like snapshotting!
You are right, if you are directly modifying the mmaped region. I always internally model my data as staging my changes to be synchronized to the mmaped region, so thats my mistake there.
> the page is either unwritable or CoW.
This is not universally true, or maybe I'm confused on this statement. MAP_SHARED exists, but maybe you are referencing a specific kernels' implementation on how they achieve coherence between file backed shared memory regions in two processes? Im not sure.
> Darwin kernel does though.
Sure we can always point to a kernel that has has implemented some feature or another, which is why I said typically you don't see it.