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No one said Apple engineers were sane! OS X throws data pages (aka anonymous pages) into the swap files on disk in order to bring in more buffer cache pages, even when it should probably be preferring to leave them in RAM. Stuff like time machine, LR, image folder browsing, and etc. reads lots of disk pages into RAM and, in the process, kick out lots of data pages. When this happens applications can hang for a bit when they needed those data pages - until they can be brought back in from the swap files. It is NOT [exclusively] the case that when the number of pages on the free list falls below a threshold (determined by the size of physical memory), the pager attempts to balance the queues like one would expect a paging mechanism to behave. Instead, OS X is constantly moving inactive list entries over to the free list entries all the freaking time. App quits, window closes, even image slide show like allocations trigger the behavior. The result is that the end user can for example, open a folder of say, 500 images and have to wait about 5 seconds for all the icons to render, close the window, open another, and when they go back to the first one they still have to wait again for all the icons to update - again. With the dynamic pager unloaded from the kernel the second time the folder is opened the display is instant. And it stays that way for hours. It will eventually unload by other mechanisms but not in seconds or minutes as the dynamic pager does.
Edited on Feb 08, 2013 at 08:12 AM · View previous versions