The Pankian Metaphor 3098

Demand-paging when done properly, is one way of conserving RAM and reducing startup overhead. It means that only the megabyte of code actually being used by the 34-megabyte executable needs to be loaded.

Initial paging activity can be "annoying" as there are no hints in the executable and the paging-in of executable occurs with program initialisation. (I feel a bleeding-obvious Patent coming on.) There's some reliance on the system's read-ahead, either at software or hardware level, to reduce the number of physical IO.

It would be advantageous for the system to get some hint of which code sections are initialisation, "kernel" and discretionary. Initialisation code would be the stuff that only needs to run "once" at program start so the system can load all of that and the "kernel" section in "one" IO. The pages occupied by initialisation can be allowed to be replaced earlier than those that are "kernel" which should be least-likely to be replaced; and the discretionary that can be aged at a nominal rate after last access.

If somebody makes a mistake in hinting a code segment, then it'll still run; possibly as a memory hog or as a demand-paging IO hog, should memory be short. The default for any code section would be "discretionary"; perhaps over-rideable by a system administrator.

Demand-paging should not prevent a running program from being "replaced". Copy-on-write or unlink paradigms exist to deal with the situation.

-- "Bernd Felsche - Innovative Reckoning, Perth, Western Australia ASCII ribbon campaign "Laws do not persuade just because X against HTML mail they threaten." and postings Lucius Annaeus Seneca, c. 4BC - 65AD.