Further to the comments about the pager hammering the disk to read clean pages (mainly but not exclusively binaries) even if swapping is disabled: In many cases adding swap space will reduce the amount of paging which occurs.

Many long-lived processes are completely idle (when was the last time that `getty ttyv6` woke up?) or at a minimum have pages of memory which are never used (e.g. the bottom page of main's stack). Evicting these "theoretically accessible but in practice never accessed" pages for memory frees up more memory for the things which matter.

Unfortunately enabling swap in linux has a very annoying side effect, linux will preferentially push out pages of running programs that have been untouched for X time for more disk cache, pretty much no matter how much ram you have.

This comes into play when you copy or access huge files that are going to be read exactly once, they will start pushing out untouched program pages to disk, in exchange for disk cache that is completely 100% useless, even to the tune of hundreds of gigabytes of it.

Programs can reduce the problem with madvise(MADV_DONT_NEED), but that only applies to files you are mmap()ing, and every single program under the sun needs to be patched to issue these calls.

You can adjust vm.swapiness systctl to make X larger, but no matter what, programs will start to get pushed out to disk eventually, and cause unresponsiveness when activated. You can reduce vm.swapiness to 1, but if you do, the system only starts swapping in an absolute critical low ram situation and you encounter anywhere from 5 minutes, to 1+ hour of total, complete unresponsiveness in a low ram situation.

There _NEEDS_ to be a setting where program pages don't get pushed out for disk cache, peroid, unless approaching a low ram situation, but BEFORE it causes long periods of total crushing unresponsiveness.

Is there a way to enable such an option for an entire process, in the same way as e.g. ionice(1)?

Whenever I take a backup of my computer it winds up swapping everything else out to disk. Normally I'm perfectly happy letting unused pages get evicted in favor of more cache, but for this specific program this behavior is very much not ideal. I'm asking here since I've done some searching in the past and not found anything, but I'm not sure if I was using the right keywords.