On Sun, Jun 16, 2019 at 6:02 PM Wols Lists <antli...@youngman.org.uk> wrote:
> And those people who wrote your guidelines? Are they the same clueless > people who believe the twice ram rule is pure fiction? (As I said, it is > *historical* *fact*). And why should I believe people who tell me the > rule no longer applies, if they can't tell me WHY it no longer applies? > I'd love to be enlightened - why can't anybody do that? > > What we call UNIX today is an API, not an implementation, and different UNIX implementations have completely different internals. You'd be hard-pressed to find any original UNIX code in any modern UNIX. Linux was written from scratch to implement the UNIX API, but other than some header files (the subject of the SCO lawsuits) there is no UNIX code in Linux. Modern UNIXes don't map the swap pages 1:1 to RAM pages like the original UNIX code did. Instead they only map the pages that actually need to be swapped. And some pages, such as executable code, don't get swapped at all - instead the existing on-disk executable file or shared library file is used as the "swap". Code and static data pages are also shared between processes, saving even more RAM. For example, per IBM for AIX ( https://developer.ibm.com/articles/au-aix7memoryoptimize3/): "A more sensible rule is to configure the paging space to be half the size of RAM plus 4GB with an upper limit of 32GB. In systems with more than 32GB of RAM, or on systems where you are using LPAR and WPAR to help split your workload, you can be significantly more selective and specific about your memory requirements." -- Manuel A. McLure WW1FA <man...@mclure.org> <http://www.mclure.org> ...for in Ulthar, according to an ancient and significant law, no man may kill a cat. -- H.P. Lovecraft
