Hadoop2: How to configure hadoop to use partial amount of resources

[Xenia Demetriou <xe...@gmail.com>]

I use a server with 16 cores, 64 GB ram, 2.5 TB disk and I want to execute
a Giraph program. I have installed hadoop-2.7.2 and I don't know how can
configure hadoop to use only a partial amount of server resources because
the server used by many users. *Requirements:* Hadoop must use max 12 cores
(=> 4 cores for NameNode, DataNode, JobTracker, TaskTracker and max 8 for
tasks) and max 28GB ram (i.e., 4*3GB + 8*2GB).

My Yarn-site resources configuration:

<property>    <name>yarn.nodemanager.resource.memory-mb</name>
<value>28672</value><description>Physical memory, in MB, to be made
available to running containers</description></property>
<property>    <name>yarn.nodemanager.resource.cpu-vcores</name>
<value>12</value>    <description>Number of CPU cores that can be
allocated for containers.</description></property></configuration>

When I try to execute Giraph program, in http://localhost:8088 Yarn
Application state is: ACCEPTED: waiting for AM container to be allocated,
launched and register with RM.

What configurations must to have in my Yarn-site.xml in order to adapt the
above requirements?
Thank you in advance.