On Tue, Feb 08, 2005 at 12:06:14PM -0500, jon ross wrote: > I have an app with a small fixed memory footprint that does a lot of > random reads from a large file. I thought if I added more memory to > the machine the VM would do more caching of the disk, but added memory > does not seem to make any difference. I played with some of the params > in /proc/sys/vm and none of them seem to have any effect. > > I tired both a 2.4.20 & 2.6.10 kernels with no difference. > > The machine is a Dell 2560. I tired memory configs of 512M, 1G, 4G and > the average read-times do not change.
Could we get some quant here? How small is "small"? How large is "large"? What are you measuring? What are the results? Does the app re-use the same data, or is its use a one-time deal? > Do I need to set/compile anything to allow the VM to use the memory? No, the Linux VM system should automatically cache for you. > If is was a way to tell how much memory the VM is using for a drive > cache I could at least tell if my kernel is miss-configured or my app > sucks. Check out the commands "free", "vmstat 1", "top", the contents of /proc/meminfo, the output of Sysrq-M. Most likely is that your app isn't behaving in a cache-friendly way. If your file will fit in memory, just fault it in sequentially (wc -l file) and then your app should cook. If you're not going to fit in memory, the vm caching will probably only help if you have some reuse; you could develop a pre-faulter to get your IO started ahead of time, but that's generally nontrivial. -andy - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
