In the case that memory is allocated and its known that it (almost certainly / probably) won't be used for a long time, it could be useful to tag this memory to be more aggressively moved into swap-space.
Is there some command to tell the kernel of this?
Failing that, it may be better to dump these out to temp files, but I was curious about the ability to send-to-swap (or something similar).
Of course if there is no swap-space, this would do nothing, and in that case writing temp files may be better.
You can use the madvise call to tell the kernel what you will likely be doing with the memory in the future. For example:
madvise(base, length, MADV_SOFT_OFFLINE);
tells the kernel that you wont need the memory in quesion any time soon, so it can be flushed to backing store (or just dropped if it was mapped from a file and is unchanged).
There's also MADV_DONTNEED which allows the kernel to drop the contents even if modified (so when you next access the memory, if you do, it might be zeroed or reread from the original mapped file).