On 30 Jan 2005 at 21:59, A-NO-NE Music wrote: > I just bought G5 Dual-2.5, which comes with only 512MB. I bought 1GB > to make it 1.5GB (still not enough, but I am running out of my > budget!). > > Just for my curiosity, I compared FinMac's vm amount before/after > adding 1GB. The result was very interesting. > > <http://www.a-no-ne.com/music/finale/vm/> > > vm is bigger after I added 1GB even though %MEM is way smaller as > expected, now why is that? The every test was done after powercycle, > of course.
A good VM should be prepared to swap out all the active memory if necessary. Thus, the swap file needs to be larger the more RAM you have. I actually keep my swap file at a minimum size of 2X my physical RAM which is 768MBs). This means that the file space is already allocated, so that when swapping needs to happen, all the VM needs to do is write to a pre-existing file. If the swap file were not pre- allocated, the file space would then have to be allocated before the swap could take place (assuming the already allocated file space were not sufficient for the swap to take place). Keep in mind, also, that for safety's sake, the RAM can't be cleared until the VM has verified successful write of the data pages to the swap file. And when data is being swapped from disk to RAM, it can't be cleared from the swap file until there's been verification that the RAM has been successfully populated with the pages swapped in. That means that to swap a 100MB process, you need 100MBs of RAM allocated to it overlapping a time period when you also need 100MBs of swap file allocated on disk. That means you need 200MBs total of RAM + swap space for short periods of time during the actual swap. Of course, all of this is highly dependent on the design of a particular VM. In the old days of the Win3.1x VM, performance *improved* with a smaller swap file once RAM exceeded 16MBs. This was because the VM was very inefficient in managing large swap files and the management of a 16MB RAM + 32MB swap file slowed the system down more than the swapping required in a 16MB RAM + 4MB swap file. It was counterintuitive, and also contradicted the VM's default settings (which was always to allocate 2X the RAM to the swap file, up to a certain percentage of free disk space). The Win95 VM system was vastly improved, and it worked better with default settings with the exception of setting a minimum swap file size. The Win NT VM seems very similar in terms of operation -- you just don't have to worry about it, other than, perhaps, choosing as I do to set a minimum swap file size (I also tend to split the swap file between drives where possible, keeping part on the same drive as the OS and most of it on a second drive; one gets a performance benefit from this if the two drives are physically different drives, but one also benefits from keeping lots of free space on the OS partition when the drives are actual volumes in a single physical disk drive). But I'm not surprised about what you report. It seems perfectly sensible. -- David W. Fenton http://www.bway.net/~dfenton David Fenton Associates http://www.bway.net/~dfassoc _______________________________________________ Finale mailing list [email protected] http://lists.shsu.edu/mailman/listinfo/finale
