Thanks Tilghman, My simplification was obviously to simple minded :) I will work this into the text.
><> ... Jack Whatever you do, work at it with all your heart... Colossians 3:23 "You don't manage people; you manage things. You lead people." — Admiral Grace Hopper, USN "If you are not part of the solution, you are part of the precipitate" - Henry J. Tillman "Anyone who has never made a mistake, has never tried anything new." - Albert Einstein On Wed, Jun 13, 2012 at 11:09 AM, Tilghman Lesher <[email protected]> wrote: > On Wed, Jun 13, 2012 at 9:22 AM, Jack Coats <[email protected]> wrote: >> I have typed my notes about Tilghman's presentation on swap on line. >> Look at the 'past presentations' section of nlug.org and the >> presentation is linked there. I might post it the link and link to my >> python notes once they are done to the mailing list. > >> https://sites.google.com/site/sycamoretechnology/linux-tips/nlug-swap > > Let me fix up some things that aren't quite right. > > Swap isn't where virtual memory lives; rather, it's an area which > allows physical memory to be extended. It's somewhat difficult to put > into simple terms, because swap today isn't the same as what swap used > to be. At one time, on some systems, your entire virtual memory was > available on disk, and only a subset of pages appeared in physical > memory, as they were needed. Currently, virtual memory is an > abstract, and some areas of virtual memory may be neither in physical > memory, nor in swap, because they are unused. Only parts of virtual > memory that are in use may appear in swap currently. > > Physical memory may be used for both virtual memory, as well as > filesystem caching. 'Swappiness' is what controls how the kernel > manages how much of each is in physical memory (not as a direct > proportion, but rather as a metric to decide whether to dump cache or > swap a process out) when memory is requested but not immediately > available. You can think of it as a percentage, in terms of: when > the kernel needs memory, and physical memory is all in use, then the > kernel will swap a process out to disk (the swap area) N percent of > the time (where N is the current swappiness value). [In actuality, it > is not this simple, because if filesystem cache gets very small, then > the kernel will thrash, and the kernel developers do a good job of > ensuring that that problem doesn't surface when swap is available.] > > Also, 0 for the swappiness value is fine, as long as your processes in > total never allocate as much physical memory as you have. If you're > running a very strict system, and memory leaks aren't an issue, you > can be perfectly fine with 0. If you ever do run out of physical > memory for process space, with a swappiness value of 0, the dreaded > OOM killer will be used to free some space. [Again, I'm > oversimplifying for comprehension.] > > -Tilghman > > -- > You received this message because you are subscribed to the Google Groups > "NLUG" group. > To post to this group, send email to [email protected] > To unsubscribe from this group, send email to > [email protected] > For more options, visit this group at > http://groups.google.com/group/nlug-talk?hl=en -- You received this message because you are subscribed to the Google Groups "NLUG" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/nlug-talk?hl=en
