Shane: My understanding is that the swap-cache is merely a different "state" Shane: of pages in the page-cache.
That's correct. Anonymous pages (=those that do not have a file backing e.g. belong to an executable file or shared library) that are considered not frequently used get a swap slot assigned before paging them out. At this point in time they are considered swap cache. Now the page gets written out and eventually removed from memory due to demand for other content. Once the page gets accessed again, we read it and consider it swap cache: if it needs to be removed from memory again, but has not changed since reading from disk, we can save the I/O to write it out and just recycle the memory page. Once swap space is 50% full Linux frees swap slots on paging in. In this case, those pages are considered anonymous again (not swap cache). By doing so, Linux avoids the potential problem that swap space runs full by potentially having more page-out I/O to the swap target (performance degradation). with kind regards Carsten Otte IBM Linux Technology Center / Boeblingen lab -- omnis enim res, quae dando non deficit, dum habetur et non datur, nondum habetur, quomodo habenda est ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390 ---------------------------------------------------------------------- For more information on Linux on System z, visit http://wiki.linuxvm.org/
