[NTLUG:Discuss] why swap?

[Stephen Klein]

I'm not sure why rsync would be running slow, but my experience is that 
2.4.X kernels tend to us at least a little swap not matter what the 
actual memory utilization is.  2.6.X kernels may be similar.

In fact, my machine shows no processes swapped out, yet free shows about 
38MB swap in use and 29MB free RAM.

Probably harmless.

Hope this helps,
Stephen Klein

Robert Citek wrote:
> 
> Why is swap being used?
> 
> I'm running rsync to take a snapshot of one machine to another.  It's 
> been proceeding extremely slowly (< 5 MB/s over GigE).  So I had a look 
> at the processes and memory usage with top, ps, and vmstat (see below). 
>  Both top and vmstat indicate that swap is being used.  Yet, the top 5 
> programs use up a total of less than 20% of memory according to top and 
> ps.  With 4 GB of RAM you'd think there would be no need to swap.
> 
> Any thoughts as to why swap is being used?  Any other diagnostics I 
> should run?
> 
> Regards,
> - Robert
> 
> -----
> 
> # uname -va
> Linux subaru 2.4.20-31.9bigmem #1 SMP Tue Apr 13 17:11:51 EDT 2004 i686 
> athlon i386 GNU/Linux
> 
> # top
>  06:42:22  up 9 days, 12:18,  2 users,  load average: 3.61, 3.83, 3.84
> 99 processes: 97 sleeping, 2 running, 0 zombie, 0 stopped
> CPU0 states:   4.1% user  16.0% system    0.0% nice   0.0% iowait  79.2% 
> idle
> CPU1 states:   5.0% user  27.0% system    0.0% nice   0.0% iowait  67.2% 
> idle
> Mem:  3643768k av, 3572204k used,   71564k free,       0k shrd,  187396k 
> buff
>                    2261104k actv,  539744k in_d,   70352k in_c
> Swap: 12590248k av,  115244k used, 12475004k free                 
> 2625336k cached
> 
>   PID USER     PRI  NI  SIZE  RSS SHARE STAT %CPU %MEM   TIME CPU COMMAND
> 19575 root      15   0  348M 269M   140 S    32.3  7.5 108:04   0 rsync
>   754 ntp       15   0  2404 2404  2160 S     0.0  0.0   0:20   0 ntpd
> 20290 rwcitek   15   0  1744 1400  1176 S     0.0  0.0   0:00   1 bash
> 20374 root      15   0  1284 1284   972 R     0.3  0.0   0:00   1 top
>   ...
> 
> # ps uax --sort=-vsz
> USER       PID %CPU %MEM   VSZ  RSS TTY      STAT START   TIME COMMAND
> root     19694 18.1  8.7 363312 320476 pts/1 S    Sep09 102:54 rsync -av 
> --delete ...
> root     19575  1.1  7.6 363308 277508 pts/1 S    Sep09   6:42 rsync -av 
> --delete ...
> root       601  0.0  0.0 20884  596 ?        S    Aug31   0:04 ypbind
> root       713  1.0  0.0  7276  336 ?        S    Aug31 140:05 3dmd
> rwcitek  17021  0.0  0.0  5600    4 pts/1    S    Sep08   0:00 /bin/bash
> rwcitek  20290  0.0  0.0  5592  884 pts/0    S    06:21   0:00 -bash
>   ...
> 
> # vmstat  1 20
>    procs                      memory      swap          io     system   
>    cpu
>  r  b  w   swpd   free   buff  cache   si   so    bi    bo   in    cs us 
> sy id
>   ...
>  0  2  2 113608  17852 177092 2692320   20    0   104     0 1619  2766  
> 0  8 92
>  2  0  1 113620  17956 177268 2692104   36   12   624  1748 2464  4901  
> 3 21 75
>  0  0  1 113652  17820 176952 2692604    0   32    12    32 1971  4712  
> 2 16 82
>  0  1  7 113652  17864 177172 2692380    0    0   136 36192 1611  2997  
> 2 11 87
>  0  0  0 113664  22604 176772 2687988    4   12   232  1712 1779  3004  
> 2 12 86
>  1  0  2 113664  19488 177204 2690728    0    0   100     0 2393  4313  
> 5 17 78
>  2  0  1 113672  18040 177324 2692064    0    8   104     8 1824  3630  
> 2 17 81
> 
> 
> 
> 
> 
> Regards,
> - Robert
> http://www.cwelug.org
> 
> 
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