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=== Who's available ===
=== Who's available ===


[[User:JohnCooper|John Cooper]] is your host for today.
[[User:FIXME|FIXME]] is your host for today.


The following people have also agreed to be available for testing, workarounds, bug fixes, and general discussion:
The following people have also agreed to be available for testing, workarounds, bug fixes, and general discussion:
* [[User:Chrisw|Chris Wright]]
* ''add your name here''


=== What's needed to test ===
=== What's needed to test ===
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=== Test Cases ===
=== Test Cases ===


This is the procedure I used to create the initial patch which allows libvirt to recognize/generate a huge page backed guest xml definition.  NB: While fairly low-level and useful to unit test, it is however not a mechanism directly visible to a typical user.
Things to test, roughly in dependency order:
 
The goal here was to allow libvirt to request guest backing by huge pages, which are essentially of 2MB size vs. that of a standard 4KB page.  Doing so offers a significant performance benefit in certain application scenarios.
 
==== Prepare the Host ====
 
Populate the huge page pool of a size suitable to support the guest image(s) which will be created:
 
    # grep Huge /proc/meminfo
    HugePages_Total:      0
    HugePages_Free:       0
    HugePages_Rsvd:        0
    HugePages_Surp:        0
    Hugepagesize:      2048 kB
    # echo 500 > /proc/sys/vm/nr_hugepages
    # grep Huge /proc/meminfo
    HugePages_Total:    500
    HugePages_Free:      500
    HugePages_Rsvd:        0
    HugePages_Surp:        0
    Hugepagesize:      2048 kB
 
Note the above may take a considerable amount of time on a machine with fragmented physical
memory.  So it is best to do so as soon after boot as possible.  Also on machines with limited
memory, populating a smaller number of pages may be necessary.
 
Having created the free huge page pool, mount hugetlbfs on the host.  If the mount point doesn't exist, create it first:
 
    # mkdir /dev/hugepages
    # mount -t hugetlbfs hugetlbfs /dev/hugepages
 
Note the mount above must be in place before launching libvirtd as the daemon currently checks
for a hugetlbfs mount only upon startup.  So if the daemon is currently running, restart it:
 
    # service libvirtd restart
 
Look in <code>/var/log/messages</code> for any errors.
 
==== Launch the Guest ====
 
To launch the guest conventionally from virsh:
 
    # virsh define test-guest.xml
    Domain foo defined from test-guest.xml
 
In the above example the guest is tagged with the name "foo" in the associated XML definition:
 
    # virsh list --all
    Id Name                State
    ----------------------------------
      - foo                  shut off
 
The guest may be launched via:
 
    # start foo
    Domain foo started
 
And a VNC connection to the guest console can be made via:
 
    # virt-viewer foo
 
If all goes well the guest should launch successfully with its image backed by huge pages.  [Note it won't unless the guest XML definition specifies huge page usage correctly as below.  But proceeding here is instructive in any event.]
 
Successful launch of a huge page backed guest may be evidenced by observing the huge page free pool decreasing:
 
    # grep Huge /proc/meminfo
    HugePages_Total:    500
    HugePages_Free:      481
    HugePages_Rsvd:      247
    HugePages_Surp:        0
    Hugepagesize:      2048 kB
 
In the likely case HugePages_Free == HugePages_Total take a look at the XML definition for the guest, For example:
 
    # virsh dumpxml foo
    <domain type='qemu'>
      <name>foo</name>
      <uuid>4c58c2a6-1b52-688e-bcfb-e57159f50961</uuid>
      <memory>524288</memory>
      <currentMemory>524288</currentMemory>
      <vcpu>1</vcpu>
      <os>
        <type arch='x86_64' machine='pc'>hvm</type>
        <boot dev='hd'/>
      </os>
        :
 
The above does not specify a memory backing mechanism and therefore defaults to backing by
4KB pages.  To specify huge page backing a &lt;memoryBacking&gt; clause is needed:
 
    # virsh dumpxml foo
    <domain type='qemu'>
      <name>foo</name>
      <uuid>4c58c2a6-1b52-688e-bcfb-e57159f50961</uuid>
      <memory>524288</memory>
      <currentMemory>524288</currentMemory>
      <memoryBacking>
        <hugepages/>
      </memoryBacking>
      <vcpu>1</vcpu>
      <os>
        <type arch='x86_64' machine='pc'>hvm</type>
        <boot dev='hd'/>
      </os>
        :
 
To add this to the XML definition, edit the corresponding file to add the &lt;memoryBacking&gt; clause as above use <code>virsh edit</code>:
 
    # virsh edit foo
    Domain foo XML configuration edited.
 
This should result in a huge page backed guest launch which may be verified as above.
 
==== Possible Caveat ====


There was a modification to the default disposition of selinux genfscon fs types affecting (among others) hugetlbfs in the kernel 2.6.29-2.6.30 timeframe.  This manifests as failure of chcon(1) on hugetlbfs files. Correction requires a selinux policy change for hugetlbfs and a corresponding kernel fs change.  Neither of which have been conclusively tested as of this writing on prospective FC12.  Thus there is a possibility SELINUX may need to be disabled to allow successful launch of a huge page backed guest.
{{admon/note|FIXME|List test cases for the feature.}}


=== Issues that were identified ===
=== Issues that were identified ===
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| Tester || Description || Bug references || Status
| Tester || Description || Bug references || Status
|-  
|-  
| caiqian || Huge Page Backed Memory Failed for Kqemu Guests || [http://bugzilla.redhat.com/527670 #527670] || '''NEW'''
| || || [http://bugzilla.redhat.com/XXXXXX #XXXXX] || '''ASSIGNED'''
|}
|}


[[Category:Fedora_12_Test_Days]]
[[Category:Test Days]]
[[Category:Virtualization]]
[[Category:Virtualization]]
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