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The real question is why those pages are being held in RAM. If they're needed, swapping them out will induce latency. I'd they're a leak or not needed, the application should be fixed to not allocate swathes of RAM it does not use.

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There are some systems which are memory-bound by nature, not as a consequence of poor optimisation, so it's not really as simple as "needed" or "not needed". As a basic example, in compression, more memory available means that we can use a larger window size, and therefore have the opportunity to achieve higher compression ratios. There are plenty of more complex examples -- a lot of mapreduce work can be made more efficient with more memory available, for example.

Indeed. None of the above are typically used (as in most of the time) on desktop systems where swap is the most problematic. As for compession, the only engine I know of that wants more than 128 MB of RAM is lrzip and other rzip derivatives.

Common offenders that bog down the system in swap for me as a developer are the web browser, JVM (Android) and electron based apps (messengers, two).

I would also like a source that substantiate the claim that using swap in map-reduce workloads actually helps. Or perhaps in database workloads. Or on any machine with relatively fixed workload.

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