site_archiver@lists.apple.com Delivered-To: darwin-kernel@lists.apple.com Check out the comments associated with VM_OBJECT_CACHE in the following file: <http://www.opensource.apple.com/source/xnu/xnu-1456.1.26/osfmk/vm/vm_object.c> S+E -- Quinn "The Eskimo!" <http://www.apple.com/developer/> Apple Developer Relations, Developer Technical Support, Core OS/Hardware At 15:16 +1100 15/1/10, Godfrey van der Linden wrote: What is the "Object cache" reported by vm_stat I believe [1] this is a cache of vm_object_t objects whose reference counts have hit zero but which persist in the hope that they get reused. For example, if you map a file, the kernel creates a vm_object_t to represent the file to the VM subsystem. If you unmap it, the vm_object_t's reference count would drop to zero, but the object would persist in the cache. If you then immediately remapped it, it wouldn't need to recreate that object (saving both the object creation time and preserving the resident pages associated with the object). and why is its hit-rate so low? I don't understand the dynamic behaviour of the VM subsystem well enough to answer that question. I will note that the cache is pretty small (vm_object_cached_max defaults to 512). [1] I don't have time to trace the logic from vm_stat to this vm_object_t cache, but I'm pretty confident about that this is what it's talking about. _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel@lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists.a... This email sent to site_archiver@lists.apple.com