Messages in this thread | | | Date | Wed, 26 May 2004 10:23:32 +0100 | From | John Bradford <> | Subject | Re: why swap at all? |
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Quote from Roger Luethi <rl@hellgate.ch>: > On Wed, 26 May 2004 02:38:23 -0400, Anthony DiSante wrote: > > Now I buy another 256MB of ram, so I have 512MB of real memory. Why not > > just disable my swap completely now? I won't have increased my memory's > > size at all, but won't I have increased its performance lots? > > > > Or, to make it more appealing, say I initially had 512MB ram and now I have > > 1GB. Wouldn't I much rather not use swap at all anymore, in this case, on > > my desktop? > > Swap serves another (often underrated) purpose: Graceful degradation. > > If you have a reasonably amount of swap space mounted, you will know > you are running out of RAM because your system will become noticeably > slower. If you have no swap whatsoever, your first warning will quite > possibly be an application OOM killed or losing data due to a failed > memory allocation. > > Think of the slowness of swap as a _feature_.
There is a very negative side to this approach as well, especially if users allocate excessive swap space.
A run-away process on a server with too much swap can cause it to grind to almost a complete halt, and become almost compltely unresponsive to remote connections.
If the total amount of storage is just enough for the tasks the server is expected to deal with, then a run-away process will likely be terminated quickly stopping it from causing the machine to grind to a halt.
If, on the other hand, there is excessive storage, it can continue running for a long time, often consuming a lot of CPU.
When the excess storage is physical RAM, this might not be particularly disasterous, but if it's swap space, it's much more likely to cause a serious drop in performance.
For a desktop system, it might not be a big deal, but when it's an ISP's server in a remote data centre, it can create a lot of unnecessary work.
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