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From "Arun C Murthy (Updated) (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (MAPREDUCE-3205) MR2 memory limits should be pmem, not vmem
Date Wed, 26 Oct 2011 07:03:32 GMT

     [ https://issues.apache.org/jira/browse/MAPREDUCE-3205?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Arun C Murthy updated MAPREDUCE-3205:
-------------------------------------

    Status: Open  (was: Patch Available)

Todd, the patch looks good. 

Some comments:
# vmem.to.pmem.limit.ratio should we vmem-pmem-limit-ratio (better vmem-pmem-ratio :) ) to
be more consistent with our current naming scheme.
# Should we default the ratio to 1.0 to be compatible with current CS in 0.20?
# Do you want to make resource.memory-gb as resource.memory-mb i.e. incorporate MAPREDUCE-3266?
# The 80% limit on available RAM needs to be more conservative? I shudder to think it probably
should be configurable...
# Might be helpful to add both pmem and vmem in error msgs for both exceptional conditions
for users?
                
> MR2 memory limits should be pmem, not vmem
> ------------------------------------------
>
>                 Key: MAPREDUCE-3205
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-3205
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: mrv2, nodemanager
>    Affects Versions: 0.23.0
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>         Attachments: mr-3205.txt, mr-3205.txt, mr-3205.txt, mr-3205.txt, mr-3205.txt
>
>
> Currently, the memory resources requested for a container limit the amount of virtual
memory used by the container. On my test clusters, at least, Java processes take up nearly
twice as much vmem as pmem - a Java process running with -Xmx500m uses 935m of vmem and only
about 560m of pmem.
> This will force admins to either under-utilize available physical memory, or oversubscribe
it by configuring the available resources on a TT to be larger than the true amount of physical
RAM.
> Instead, I would propose that the resource limit apply to pmem, and allow the admin to
configure a "vmem overcommit ratio" which sets the vmem limit as a function of pmem limit.

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