On Sat, Nov 29, 2008 at 2:37 PM, Bob Friesenhahn < [EMAIL PROTECTED]> wrote:
> > To be more clear, memory which is claimed to be free is often actually > still used for caching. Even if the virtual memory system has not > mapped a VM page to a process, if a minor page fault occurs (due to an > access), the data in that seemingly "unused" page may still be > immediately switched in and used because the VM system tracks where > the current content of that page came from. This is primarily the > case for memory-mapped regions such as ordinary files, shared > libraries, executable text, or even a video frame buffer. This is > pretty much normal operation since when new processes are started, the > VM maps the existing pages that the new process requires into its > address space. > > It is pretty common for Unix systems to lie about free memory and use > that free memory for the filesystem cache with the expectation that > this "free" memory can be freed up for use fast enough that no one > really notices. > > If the critical "working set" of VM pages is larger than available > memory, then the system will become exceedingly slow. This is > indicated by a substantial amount of major page fault activity. > Since disk is 10,000 times slower than RAM, major page faults can > really slow things down dramatically. Imagine what happens if ZFS or > an often-accessed part of the kernel is not able to fit in available > RAM. > > Bob > ====================================== > Bob Friesenhahn > [EMAIL PROTECTED], http://www.simplesystems.org/users/bfriesen/ > GraphicsMagick Maintainer, http://www.GraphicsMagick.org/ > > So as a follow on to this, I guess my question is: Can you shut down the linux box and throw the ram from it into this box and see what kind of performance you are getting? I believe you'll see far, far better results with 1.5G in the system. --Tim
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