Our QA noticed no new builds for 2 days. When I checked the polling log of one project it was:

Perforce Polling Log

Started on Apr 1, 2012 7:00:38 PM
Looking for changes...
Using master
Using master perforce client: jenkins_me-main
ERROR: Failed to record SCM polling
java.lang.OutOfMemoryError: Java heap space

I did not follow the Jenkins wiki process . If this happens again, I'll use it to get more information. Here is the stack trace:

Apr 1, 2012 7:48:48 PM hudson.triggers.SCMTrigger$Runner runPolling
SEVERE: Failed to record SCM polling
java.lang.OutOfMemoryError: Java heap space
at hudson.remoting.FastPipedInputStream.<init>(FastPipedInputStream.java:78)
at hudson.remoting.FastPipedInputStream.<init>(FastPipedInputStream.java:66)
at hudson.plugins.perforce.HudsonP4RemoteExecutor.exec(HudsonP4RemoteExecutor.java:97)
at com.tek42.perforce.parse.AbstractPerforceTemplate.getPerforceResponse(AbstractPerforceTemplate.java:321)
at com.tek42.perforce.parse.AbstractPerforceTemplate.getPerforceResponse(AbstractPerforceTemplate.java:292)
at com.tek42.perforce.parse.Workspaces.getWorkspace(Workspaces.java:54)
at hudson.plugins.perforce.PerforceSCM.getPerforceWorkspace(PerforceSCM.java:1208)
at hudson.plugins.perforce.PerforceSCM.compareRemoteRevisionWith(PerforceSCM.java:903)
at hudson.scm.SCM._compareRemoteRevisionWith(SCM.java:356)
at hudson.scm.SCM.poll(SCM.java:373)
at hudson.model.AbstractProject.poll(AbstractProject.java:1323)
at hudson.triggers.SCMTrigger$Runner.runPolling(SCMTrigger.java:420)
at hudson.triggers.SCMTrigger$Runner.run(SCMTrigger.java:449)
at hudson.util.SequentialExecutionQueue$QueueEntry.run(SequentialExecutionQueue.java:118)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:441)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:662)

We do keep Jenkins running without periodic reboots so I'm thinking there may be a memory leak somewhere as well.