p4 java out of memory exception, stack trace is below. I've worked around this on a couple of slaves by using java64, I'll probably investigate it as well and push up a fix if I track one down but thought I'd pass it on since it adds quite a bit of effort to getting a default jenkins machine master or slave working with decent size depots.

last jenkins console output:
P4 Task: cleaning workspace to match have list.
... p4 reconcile -w -f -m D:\jenkins\Swarm/...
-
p4 reconcile -w -f -m D:\jenkins\Swarm/...

P4 Task: attempt: 1
P4 Task: failed: com.perforce.p4java.exception.ConnectionException: Java heap space
ERROR: P4 Task: failed: com.perforce.p4java.exception.ConnectionException: Java heap space
Archiving artifacts
Creating image galleries.Creating archived images gallery.Recording plot data
Finished: FAILURE

stack trace:
Nov 20, 2015 10:31:40 AM org.jenkinsci.plugins.p4.tasks.AbstractTask tryTask
SEVERE: P4 Task: attempt: 1
com.perforce.p4java.exception.ConnectionException: Java heap space
at com.perforce.p4java.impl.mapbased.rpc.packet.RpcPacketDispatcher.dispatch(RpcPacketDispatcher.java:225)
at com.perforce.p4java.impl.mapbased.rpc.OneShotServerImpl.execMapCmdList(OneShotServerImpl.java:350)
at com.perforce.p4java.impl.mapbased.rpc.OneShotServerImpl.execMapCmdList(OneShotServerImpl.java:199)
at com.perforce.p4java.impl.mapbased.server.Server.execMapCmdList(Server.java:5149)
at com.perforce.p4java.impl.mapbased.client.Client.reconcileFiles(Client.java:1593)
at org.jenkinsci.plugins.p4.client.ClientHelper.tidyClean(ClientHelper.java:358)
at org.jenkinsci.plugins.p4.client.ClientHelper.tidyAutoCleanImpl(ClientHelper.java:285)
at org.jenkinsci.plugins.p4.client.ClientHelper.tidyWorkspace(ClientHelper.java:245)
at org.jenkinsci.plugins.p4.tasks.CheckoutTask.task(CheckoutTask.java:97)
at org.jenkinsci.plugins.p4.tasks.AbstractTask.tryTask(AbstractTask.java:216)
at org.jenkinsci.plugins.p4.tasks.CheckoutTask.invoke(CheckoutTask.java:91)
at org.jenkinsci.plugins.p4.tasks.CheckoutTask.invoke(CheckoutTask.java:28)
at hudson.FilePath$FileCallableWrapper.call(FilePath.java:2720)
at hudson.remoting.UserRequest.perform(UserRequest.java:121)
at hudson.remoting.UserRequest.perform(UserRequest.java:49)
at hudson.remoting.Request$2.run(Request.java:326)
at hudson.remoting.InterceptingExecutorService$1.call(InterceptingExecutorService.java:68)
at java.util.concurrent.FutureTask.run(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at hudson.remoting.Engine$1$1.run(Engine.java:69)
at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.OutOfMemoryError: Java heap space
at com.perforce.p4java.impl.mapbased.rpc.func.helper.MD5Digester.digestStream(MD5Digester.java:177)
at com.perforce.p4java.impl.mapbased.rpc.func.helper.MD5Digester.digestFileAs32ByteHex(MD5Digester.java:337)
at com.perforce.p4java.impl.mapbased.rpc.func.helper.MD5Digester.digestFileAs32ByteHex(MD5Digester.java:302)
at com.perforce.p4java.impl.mapbased.rpc.func.client.ClientSystemFileCommands.reconcileEdit(ClientSystemFileCommands.java:1681)
at com.perforce.p4java.impl.mapbased.rpc.func.client.ClientFunctionDispatcher.dispatch(ClientFunctionDispatcher.java:194)
at com.perforce.p4java.impl.mapbased.rpc.packet.RpcPacketDispatcher.dispatch(RpcPacketDispatcher.java:160)
... 21 more
Nov 20, 2015 11:13:25 AM org.jenkinsci.plugins.p4.tasks.AbstractTask tryTask