4 ms·

Be sure to check PHK's comment (#5) madvise + mincore syscalls could be used to get the kernel to preload the pages asynchronously.

• wmf 16y ago
  Not really; because mincore() does not generate events you'd have to poll to find out when the page-in has finished, which seems pretty wasteful. If I was doing disk I/O from an event-driven program I would rather use the Flash approach of using a small number of worker threads to perform blocking I/O. PHK says "I consider this a deficiency in POSIX standards, not in the concept of VM.", but you have to go to production with the kernel you have, not the kernel you wish you had.
  • ntoshev 16y ago
    I agree you have to make it work with the real and not ideal kernel :) Another thing PHK misses is that single-threaded approach solves the database concurrency problems for free, and people start to use it more - e.g. Stonebraker in his VoltDB. Polling mincore wouldn't be that bad as it would only happen between the commands and at least the core of the algorithm would be simple: before executing a command, check if it's data are in memory with mincore, if not ask to load them with madvise, and go to the next command. What does Flash use worker threads for?
    • wmf 16y ago
      Flash used worker threads for any operation that could potentially block, like disk reads. http://www.usenix.org/event/usenix99/full_papers/pai/pai_html/paper-html.html http://www.usenix.org/event/usenix99/full_papers/pai/pai_htm...