> From: tech-boun...@lists.lopsa.org [mailto:tech-boun...@lists.lopsa.org] > On Behalf Of Andrew Hume > > err, that is the whole point. > SwapTotal - SwapFree reflects the high water mark problem. > for example, if we are swapping, and process P1 has 20GB of swap, > then SwapTotal - SwapFree = 20GB. if i start a new process P2 which uses
OMG, holy crap. I don't care how big your processes are, or how much memory you have in your system, you should never be swapping active memory. You can always solve this problem by either adding more memory, or using a memory mapped file in your process. If it is a given, that you have a process that will consume more active storage than what's physically in your system, then the memory mapped file is much more desirable over swapping, because if you allow the system to swap the active memory, you will force all the useful cache out of cache, and you will force all the other active processes in the system to swap out, grinding the system to a near-halt. So badly, that often, it appears the system has halted, and processes and network connections begin to timeout and fail. The reliability and performance of a system swapping active is far worse than the reliability and performance of a system with a couple of processes using memory mapped files. That's an inappropriate use for swap. Here is what swap is meant for: At every opportunity, the kernel will grow the system buffer & cache to consume all physical memory in the system. It is normal to see near-zero "free" memory in the system, provided that you have a large cache & buffer. If you give some swap to the kernel, then it has an extra degree of freedom. The kernel now has freedom to choose, which it would rather lose: Some fairly cold cache, or some idle memory? It is normal for some processes to sit almost completely idle for the life of the computer. Or some process dies in a zombie state, or whatever. Swap is useful, so the kernel can push these things out of memory and use that memory for caching instead. Swapping is meant to increase performance. _______________________________________________ Tech mailing list Tech@lists.lopsa.org https://lists.lopsa.org/cgi-bin/mailman/listinfo/tech This list provided by the League of Professional System Administrators http://lopsa.org/
