On Sunday, 20 October 2019 16:03:42 BST Dale wrote: > Here's the > thing about using swap on my rig, once it does, the system gets > extremely slow. Even switching desktops can take a minute or longer. > Other than trying to get to what is eating up memory and killing it, the > system is virtually useless. Even my video stops playing.
Swapping can bring the system to its knees, but only under certain operating scenarios. This is how I understand it works: Say you're browsing and keep opening tabs. The browser application will preemptively allocate memory for more tabs, in case you carry on opening even more tabs. Then you open yet another big application in terms of memory usage and start running it. The kernel will reallocate some of the browser memory not currently utilised to the other application and keep things working smoothly. With more applications/tabs being opened you will eventually run out of RAM and the kernel will swap some of the memory pages to disk. The swapping is meant to be selective, i.e. things you haven't used in a while will be taken out of RAM and saved onto your disk. Under the above scenario you may notice a momentary latency on your desktop as data is swapped onto the disk, but afterwards the desktop should be responsive once more - unless more swapping is again demanded by your actions. If you try to access an application which has had parts of its memory allocation swapped out to disk you will notice a delay in its reactions. Now, in a gentoo scenario, say a mammoth compile like Chromium, with a large count of jobs specified for it, you could end up swapping part or all of one or more jobs into memory, only to swap it out again in order to process it. The compile keeps swapping in and out a job at a time in order to carry on compiling. The disk thrashing is now continuous and indeed interacting with your desktop will be painful - potentially waiting for minutes at a time before an application responds. The way out of this bottleneck is to either increase your RAM, or minimise the use of memory by reducing the job count in MAKEOPTS. Shutting down desktop applications and login out of any desktop sessions to release RAM will also help. On a laptop with 4G RAM compiling Chromium is quite challenging when even a single gcc job could grow to 3G or more. Swapping and a disk I/O bottleneck becomes unavoidable and moving the compile of binaries to a bigger PC becomes a rather wise solution. Another occasion when swapping can cause havoc is when you have a memory leak due to some buggy application and all your RAM followed by swap is chewed up until an OOM ensues. For these reasons I always set up swap on my gentoo systems. -- Regards, Mick
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