Hi all, I'm trying to add support for demand paging to an RTOS which has basic page tables and address space management. The same page tables might be in use on different CPUs simultaneously. Even if not, all have the same virtual to physical mappings so any page ins or outs will need to modify all page tables.
Having some problems figuring out how the locking is supposed to work in an SMP environment when modifying page tables, or making decisions based on whether a page is dirty or clean. Consider the scenario where I select a page to evict from the page replacement algorithm.
- If it's a clean page I can just discard it without writing its contents out to the swap area. But I would have to atomically know that it is clean and un-map it with respect to all CPUs not just the local one. I don't see how to close the race where the page could suddenly become dirty, possibly through a stale TLB reference, on some other CPU.
- If it's a dirty page I have to initiate a transfer to write it out to swap. How do I coordinate this such that the data page is not modified on another CPU, but the local CPU can still access its data to transfer its contents to the swap area?
I had an idea where I could implement a "page table lock" API which grabs a spinlock AND sends out an IPI to all other CPUs to block until the lock is released. Essentially forcing all other CPUs to spin during the critical section but is there some other way which doesn't completely bind up the system like this?
This is all straightforward on uniprocessor where I just disable interrupts while doing stuff.
http://www.reddit.com/r/CFB/comments/2mf7l2/game_thread_florida_state_miami_800_pm_et/cm3raua
/u/delatriangle. Sorry for the mistake.
Outside from an article from Tannenbaum in the "Modern Operating Systems" I cannot find a certain fact he claims (or maybe I interpret it incorrectly).
He states: "Therefore, many paging systems try to keep track of each process' working set and make sure that it is in memory before letting the process run. This approach is called the working set model (Denning, 1970). It is designed to greatly reduce the page fault rate. Loading the pages before letting processes run is also called prepaging. Note that the working set changes over time."
Source: http://www.informit.com/articles/article.aspx?p=25260&seqNum=9
From what he says, as soon as a Working Set is established the algorithm uses prepaging to have the pages loaded before the application actually is running.
On the other hand several other sources state, for the Page Fetch Policy (which always is either Prepaging or Demand Paging) Demand Paging is used. I wonder if this is only the case for the working set if a process is initialized.
For instance we have a process just being initialized, the first pages the process requests will be put into primary/physical memory by Demand Paging. Due to multitasking a complete working set could be outsourced. Now the question is, is the working set put back into memory by Demand Paging or by Prepaging? Or is there something wrong with my terminology?
Cheers, Thomas Davies
Every time I google demand paging I just get a headline reading Demand Paging and then the text goes on explaining how the virtual memory is devided into pages, the physical memory is divided into frames ... etc.
Is demand paging the whole concept of having a virtual memory that is devided into pages? what EXACTLY is demand paging (I guess, ELI5 please?)
EDIT: I understand how the virtual memory works and what pages are used for, I just don't understand what part of it is called "demand paging"
I've read up on demand paging in my textbook, but so many different approaches and ideas were discussed that I don't think I fully grasp the idea of what's going on. I've been asked to simulate it, and I don't think I understand what it is I'm simulating.
I've been trying to read through the Linux kernel code for quite a while now and trying to figure out how the mm/filemap.c/filemap_fault() function works. I feel really intimidated since it feels like I'm going through a complex labyrinth. I do understand some part of it but I still feel scared since I don't really know what to do to complete this assignment with a kernel this complex.
Basically, I have to convert Linux's default readahead scheme memory management to a demand paging scheme.
So how can I understand a source code that is complex and feel less intimidated? Where can I go from here to understand what to do to solve this?
Hi, SaaS community,
Been lurking here for some time! This community has been pretty inspiring for me to try out creating SaaS myself.
I have a strong background in AI/ML with multiple papers published at top conferences and decided to give it a shot at making SaaS using my domain knowledge.
This product stemmed out from another SaaS that I have been developing. It required extracting the main body of text from PDFs without headings, footnotes, captions, figures, and tables. On top of that I needed to extract text in the natural human reading order. I implemented and trained the AI/ML model that manages to extract text following those requirements that works pretty well.
Now, both commercial and open-source PDF-to-text software such as AWS Textract, Pytesstract, Google Cloud OCR, etc just extracts raw text from pdf without taking into account that structure. So I thought to test out whether this solution would be useful to other folks besides myself and my original use case.
Here is the link to the landing page
I would really appreciate your general feedback on potential leads to approach who would need this solution (even better if you are interested yourself :) ) and feedback on landing page
In the meantime I want to give something back to this community and happy to answer any questions you have about AI/ML; using it & training it in practice beyond just using off-the-shelf things like GPT3 API
Hey everyone,
I recently created a landing page to test demand for a Airbnb chatbot. All feedback would be warmly welcomed. FYI, I am in the process of getting the SSL straightened out for the domain, but here is what the landing page would look like.
I want to test the product as soon as possible. Do you guys think that the UI would suffice for something like this?
To give you all some background, I used to run an Airbnb management business. The pandemic hit, and we ended up shutting down shop. I read a bunch of books about UI, Product Management, and Startups. I feel ready to take some action and get the ball rolling on solving the problems that I used to face in Airbnb management.
So, in the case of developing a physical product that may cost tens of thousands to develop even into just a proper showable prototype, how do you determine demand without a prototype and just the idea for the physical product?
Unlike software products, it would be difficult to sense any traction from a landing page without at least photos or videos of the potential product. Ideally we all want to see some traction before committing serious cash into development, but what does this mean for physical products? Making a 3D animated version of the product and showing that on a landing page? How would you go about this?
On streaming box devices, (Roku, Apple TV, Fire TV) there should be a fast way to access the dedicated live guide and on demand page for the channel or channel group you are currently watching (that you can access from the guide by highlighting the channel logo to the left) without backing out and going through the entire live guide.
Is there currently a way to do this? I use Roku, and there doesn’t seem to be a way. If you want to view the on demand page or see what is coming up next, you have to back all the way out to the live guide and scroll as far down as that particular channel is.
Pressing the up/down button to prompt the menu bar below the DVR tracking bar during live tv and letting you scroll up to highlight the current channel logo in the top left corner to click and pull up that channel’s guide and on demand selection would be an elegant solution.
Thank you for the overwhelming response I was not expecting my post to gain as much traction as it did. Thanks for all the awards and the messages. It is just amazing.
I have decided to elaborate on what I had written earlier in regard to Safemoon, it wouldn't be right if I did not follow up.
Firstly, here is a receipt of the earliest BTC transaction I could find. I have several of these so please if you want more I can upload plenty of them but I don't think this will convince people, or at this point - they wouldn't care regardless -
My address was - 12q4pAZNgh3GPSKB236q4gNTwYfpcPrMiG - which has been decommissioned.
Obviously every receipt I have corresponds with a transaction on the blockchain so you can go deeper if you're into that. I guess that is the magic of public ledger right? The significance of the technology. I mentioned this earlier remember? I will mention this again shortly as it is very relevant.
The "I'm new to crypto" post was a low-key dig at r/CryptoCurrency, to see how they would treat a new Safemoon post. It was at the time (and still is for those with a sense of humour) a joke.
Secondly, I wasn't paid to provide a opinion here. Surely for paid content they would have selected someone with a better profile history. I was merely pointing out that I believe in the technology and Safemoon has all of the features of a great currency. Sure, looking at my previous posts you'd say "this guy is way too enthusiastic, it can't be real" or something similar. But I assure you, people are looking at you everyday and probably saying the exact same thing about things you believe in. It's a bit strange, I'm also not the most extroverted being, so big outbursts and loud noises are often a way for me to communicate clearly.
There isn't much to the rest of my crypto story, I own my house and have a family and savings. This is what I meant by a comfortable life. No, I do not own a Lamborghini, nor do I have any interest in the car (I am more likely to buy a DMC-12).
...and Safemoon?
To put all of this in perspective I would have to wrap up absolutely everything I know about the technology, bundle it up nicely in a readable format - this could go on for days so if you want an opinion please just message me (nobody asked for my last one). I have chosen a few current things to mention - I'm not expecting the same volatility as my last post so once again thanks to the upvoters
... keep reading on reddit ➡
