Kirk: Last time I owned a windows box (I admit, that was quite a while ago, but it did have XP SP2, which as far as everyone is concerned is the 'latest' version of windows still, I believe), when I tried to turn swap off a whole host of apps stopped working. I then configured swap to be 50MB in size, and they started working again, but I didn't notice any significant speedup; instead, some research showed that the 50MB chunk was heavily contested. I then loaded up the old ramdisk driver to create an all-RAM disk just to satisfy XP's insistence on swap space, but that dropped the entire kernel down to 16-bit mode or some such whacky legacy support maneuvre. A year later I downloaded an XP native driver to create ram disks but never got around to trying this again.
I'm on OS X now, but I doubt turning off paging is a good idea; even if I have more than enough RAM to keep all running apps in memory, swapping unused bits out is still a useful exercise as it frees up RAM for disk caches. I wonder if the extra effort to write RAM to swap is more, or less, disk access compared to the # of accesses saved by disk caches. On Jan 1, 10:11 pm, kirk <kirk.pepperd...@gmail.com> wrote: > > A recap of issues with eating as much memory as you want: > > > FACT A: OSes manage virtual memory and make it relatively hard for > > userland apps to meddle and/or inspect this. > > > FACT B: There's no way for the JVM to see any difference between an > > app leaking memory and an app that has a legitimate use for its > > continued increased memory requirements. Even if we can somehow > > magically create a garbage collector that can do perfect cleanup in > > near zero extra time compared to the more heuristic (pretty good but > > not perfect) approach used by the current garbage collector, that > > still doesn't allow us to assume that a JVM that wants more memory > > should really get it. > > Actually... I've written about how one should be able to automagicly > detect memory leaks. Leaked objects are never accessed so if you track > access, you can find them. I had some discussions with the guy working > on the G1 collector and while there are some performance issues with > tracking references, the scheme was workable. While sorting through > details, a couple of papers came to light that detail similar schemes > for automatic leak detection. If I can work out the issue with write > barriers, this is something that could be dropped into OpenJDK.> FACT C: Its > possible to do a complete garbage collect, but this takes > > precious CPU cycles. This is worth it to avoid swapping, but it is a > > complete waste of time if the host computer has real memory to spare. > > It's not like unused memory saves power or some such. It's effectively > > a free resource, if its there. > > swap is an archaic optimization where disk is traded to create more > memory. Out machines now have more memory than one can shake a stick at. > If you've got 2-4 gigs on your machine, I'd turn swap off. I've done > this for my windows machines for a couple of years now. They have 2 gigs > of ram. Occasionally I have to turn swap back on when I'm doing > something that requires a lot of ram. However I normally use less than > 2gigs so turning off swap is no big deal. The performance boost it gives > is worth it. It also keeps my disk drive quiet which is a blessing for > the batteries in my laptops. > > Regards, > Kirk --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "The Java Posse" group. To post to this group, send email to javaposse@googlegroups.com To unsubscribe from this group, send email to javaposse+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/javaposse?hl=en -~----------~----~----~----~------~----~------~--~---
