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Comment by tiles | Hacker News Reader

Am I missing something? Does Firefox not use unused RAM for cache in a similar manner as Linux uses unused RAM?

555 MB is still a lot. That's the actual memory usage.

Modern web browser are complicated pieces of software that are also the nexus for most people's interactions with their computer. tiles' point is correct: Firefox will tend to cache things much like the OS itself. We should expect it to use a lot of memory. If your system performance has not suffered, there is no problem.

I'm sorry, but this reply doesn't make any sense to me. If applications have to cache something, they should use the file system, which would not affect their resident memory at all. Maybe I'm just old school, but where I come from operating systems handle the memory hierarchy, not applications.

They cache it in memory to avoid latency. Writing to and reading from disk increases latency. Even crossing the kernel boundary will increase latency.

Modern web browsers have architectures similar to OSes at this point - because they have requirements similar to OSes. I think it's natural that they will take on some of the same responsibilities.

Where I come from, what you're describing is called pre-fetching, not caching. That's why your earlier comment confused me.

No, I'm talking about caching: keeping data around that you have previously used, assuming you will use it again. However, in order to support caching, you must pre-allocate memory.

If it's cached to the filesystem, it'll be handled by the file cache, under the kernel's control with the rest of RAM. Maybe browser makers have a good reason for thinking they can do better than the OS, I don't know, but having two systems trying to do the same job with the same resources sounds like a recipe for instability and inefficiency to me.

If you have to cross the kernel boundary every time you want to access something in your cache, your "cache" is now much, much slower. Note that this applies even if the OS keeps the file in memory, and doesn't require going to disk.

Sure, but if accepting that cache slowdown makes the rest of the system more responsive and more useful for background tasks, it may be worthwhile. It's a trade-off, and the browser makers have every incentive to be as selfish as possible.

Performance does suffer, because the operating system doesn't know that all that memory being used by firefox is just cache. And firefox doesn't know when the operating system would like to use memory for something other than cache. So when you start a second large program, it's thrashing time.

VMs like vmware have the exact same problem, where the host might want memory used by the guest, and you end up with weird scenarios where the guest's swap is in the host's disk cache, but the guest's memory is in the host's swap. One of the things guest tools are supposed to do is communicate with the host regarding memory pressure. Firefox lacks this feedback mechanism.

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