1

Linux has a file system cache where it keeps as many data as possible in RAM as a buffer.

A thread tries to read a page block in file system. If the page is in cache, it fetches the data from the cache (cache hit). otherwise, it issues disk i/o request for the page and waits (cache miss).

But when multiple threads (or processors) read the same page block, I think there can be one more case; the page is not in cache, but the i/o request for the page is already issued. In this case, no disk i/o is issued again, but the threads should wait for the page to be read from disk anyway.

Does Linux's file cache have this property? What do you call this?

Improve this question

1 Answer 1

Reset to default
0

The way it's done in Linux, and I would think in any operating system where loading from cache is asynchronous, is: when a page is requested but not yet loaded, there is a cache entry that is flagged as not-yet-loaded. When the second request comes in, it piggybacks onto the existing cache entry and waits for the load to complete. In the Linux kernel, the mechanism to wait is called a wait queue. There's a lot of documentation out there about wait queues: Linux Device Drivers, Completions (a slightly higher-level data structure on top of wait queues), kernel API documentation, …

I don't know if this mechanism has a formal name.

Improve this answer

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .