Brian Long wrote:
On Fri, 2005-10-28 at 12:17 +0200, Leos Bitto wrote:About a year ago we found an issue with RHEL 3 AS, which we considered serious - however, when I called Red Hat support, I was assuerd that the behaviour was absolutely normal. What happened was a server with 4 CPUs, 2 GB RAM and 2 GB swap, which started swapping terribly after some disk activity appeared, and kept swapping ever since then, until we rebooted it.We have an in-house developed Java application, which is running using Sun's JVM 1.4. This application receives authentication requests from some black-box device and has to respond quickly, otherwise that black-box device considers the authentication requests failed.We were able to trigger the issue simply by analyzing some large logs using simple grep commands. What happened was that the server cached the logs in RAM and forced the application to swap and thus slow down unacceptably. What bothered us was that the application never returned to the original speed, even after we stopped accessing the logs. Even after several hours it did not recover, so we had to reboot the server.We solved it by turning off the swap - fortunatelly we had enough RAM. This way the RAM does not get filled with disk cache and the application is not forced to slow down due to swapping and everything works fine. When we tried this application on RHEL 4, it worked much better - no swapping, even with heavy disk activity.Leos, This was a problem in the original RHEL 3 settings for /proc/sys/vm/pagecache. In one of the updates, Red Hat changed the defaults to "1 15 100" (I forget the original defaults). Have you tried re-enabling swap with U6? Because of this VM setting, the newer kernels should not exhibit the behavior you describe. /Brian/
I actually tried this, and quite a few other suggestions, on RHEL3 and still experienced the problem described.
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