[CentOS] Swap Considerations
Philip.R.Schaffner at nasa.gov
Thu Mar 1 16:07:48 UTC 2007
On Thu, 2007-03-01 at 23:17 +0800, Feizhou wrote:
> It comes down to whether the use of swap has a significant effect on
> your operations. You can tell the kernel to not ever use swap unless
> absolutely necessary: swappiness = 0. Normally it is set at 60 (range
> from 0 - 100). Let me explain how I would handle swap.
> Take a case of mail servers with hundreds of processes that only have
> 1GB of RAM and a pair of disks. I would use vmstat to check the 'si
> columns to see whether the box is swapping. Positive figures in both
> columns indicates use of swap and if I see constant reports of
> figures for these two columns, I start reducing the number of
> allowed to run to increase performance. This is how I identify active
> swap usage as opposed to swap in use. Swap in use is not the same as
> active swap usage. I could get maybe tens or even hundreds of
> being reported in swap but if vmstat 'si so' columns report zeros, I
> don't worry about its effect on disk i/o because there is none.
> if the amount of swap in use continues to grow over time, I start
> looking for memory leaks.
This has been a very interesting thread, and given the length
(discounting a few digressions), and the general number of occurrences
of the subject of swap in the list archives, there is a high level of
interest in the topic. My search of the Wiki turns up nothing helpful.
Sounds like a good candidate for an entry on the Wiki FAQ page:
Anyone (like Feizhou :-) who has a through grasp of the topic willing to
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