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Comment by rishabhaiover | Hacker News Reader

it allows the program to reference memory without having to manage it in the heap space. it would make the program faster in a memory managed language, otherwise it would reduce the memory footprint consumed by the program.

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You mean it converts an expression like `buf[i]` into a baroque sequence of CPU exception paths, potentially involving a trap back into the kernel.

I don't fully understand the under the hood mechanics of mmap, but I can sense that you're trying to convey that mmap shouldn't be used a blanket optimization technique as there are tradeoffs in terms of page fault overheads (being at the mercy of OS page cache mechanics)

I think he's conveying that he doesn't know what he's talking about. buf[i] generates the same code regardless of whether mmap is being used. The first access to a page will cause a trap that loads the page into memory, but this is also true if the memory is read into.

Tradeoffs such as "if an I/O error occurs, the program immediately segfaults." Also, I doubt you're I/O bound to the point where mmap noticeably better than read, but I guess it's fine for an experiment.

An I/O error on a mmapped file causes a SIGBUS, which the program can catch and report.

And I/O bound programs are I/O bound whereas programs that aren't, aren't, so it really isn't meaningful to talk about whether "you" are I/O bound to the point that it's significant--maybe you are, maybe you aren't. I agree about experimentation.

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