# svmon -G
               size           inuse            free        pin       virtual
memory   1048576    1048277        299     243096    1166071
pg space  3481600     547806
               work       pers       clnt      lpage
pin          243096          0          0          0
in use      997529          0   50748          0

Your system behaves  somewhat strangely. I doubt it has been running the same apps with the same environment and apps parameters as before.
Without further system information it is difficult to give a solid diagnosis, but your svmon -G has told some interesting story:
1. The pinned pages is 243096 -- about 1G RAM is pinned. 1G of memory out of 4G is "taken away" from most processes.
2. When lots memory is used, you expect to see high number of pers and/or clnt pages for file caching, but the pers is 0 and clnt is only 50748 pages or 202M. i.e. No JFS is using the memory. You do have JFS2  (or NFS, CDROM) files but it  is quite small.
3. Now there is 997529 pages of working segment memory.  997529/104856 = 95%. The "computational memory" accounts for 95% of the 4G total memory ... this is very unusual. I would say that the system is using too much memory for working segments.
4. The paging space has 547806 pages in use, that is another 2G of virtual memory (this number may not be exact, as some pages may exist in RAM *and* PS).

Things to check :
1. Who has pinned all those memory? Is it by design or is it a program problem?
    do "ps aux" to catch the big memory user, and then "svmon -P pid" to see all details of the memory usage.
2. The system may have a bad memory leak? Not only unfreed mallocs can cause memory leak. You can have a memory leak (sort of) because of a process stays there and never issues or causes a memory disclaim.
    run "svmon -P pid" every so often to check it out
3. Do you by any chance have the paging space allocation mode changed to early? This could cause increased use of PS.
4. As always, make sure you have installed the latest patches for your OS level. This should have been the #1 suggestion.
5. If you need further assistance, run "svmon -P pid", also run "vmstat -I 2 10" when system is paging heavily, and post the output here.
6. Also do "vmo -a"  and "ioo -a" and attach the output. Please note that "vmtune" is no longer supported on AIX 5.3.