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Old 03-21-2014, 02:53 PM   #1
awreneau
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Registered: Aug 2003
Location: GA
Distribution: Ubuntu
Posts: 29

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calculate kernel.shmall during kickstart


I've been given a set of values for the sysctl.conf file and I'd like to incorporate those into the kickstart so there is less manual work after the image is laid down.

I can collect the memory on the box w/ this:

awk '/^MemTotal/{ print $2 }' /proc/meminfo

I'd then like to fulfill the request to adjust kernel.shmall on the fly. The request is as follows:

kernel.shmall = MemTotal size / getconf PAGE_SIZE.


I cant seem to get past the fatal division by zero problem.

Here is the actual syntax.
Code:
awk '/^MemTotal/{ print $2 / system(getconf PAGE_SIZE) }' /proc/meminfo
awk: (FILENAME=/proc/meminfo FNR=1) fatal: division by zero attempted
 
Old 03-27-2014, 09:06 AM   #2
awreneau
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Registered: Aug 2003
Location: GA
Distribution: Ubuntu
Posts: 29

Original Poster
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I figured it out.
I took an easy way out and setup a variable to pass to awk. I also had to format the output so as to eliminate any decimal places w/ the OFMT option.


Code:
#kernel.shmall physical RAM / pagesize
pgsize=$(getconf PAGE_SIZE)
sed -i "s/^kernel.shmall = .*/kernel.shmall = `awk -v pgsz=$pgsize '/^MemTotal/{print $2/pgsz}' OFMT="%3.0f" /proc/meminfo`/" /etc/sysctl.conf
 
Old 04-09-2014, 10:49 AM   #3
awreneau
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Registered: Aug 2003
Location: GA
Distribution: Ubuntu
Posts: 29

Original Poster
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So I found I'd made an error here. The MemTotal value has to be converted to bytes first bc it's in KB from /proc/meminfo. The new formula is



#kernel.shmall physical RAM / pagesize
pgsize=$(getconf PAGE_SIZE)
sed -i "s/^kernel.shmall = .*/kernel.shmall = `awk -v pgsz=$pgsize '/^MemTotal/{print $2*1024/pgsz}' OFMT="%3.0f" /proc/meminfo`/" /etc/sysctl.conf


And for giggles I'm adding the shmmax and huge page calculation.

#kernel.shmmax = 1/2 of physical ram
sed -i "s/^kernel.shmmax = .*/kernel.shmmax = `awk '/^MemTotal/{print $2*1024/2}' /proc/meminfo`/" /etc/sysctl.conf


#vm.nr_hugepages = 50% of the total memory in bytes
cat >> /etc/sysctl.conf << EOF
vm.nr_hugepages = `awk '/^MemTotal/{print $2}' /proc/meminfo | awk '{huge = $1 / 2 / 2048} {printf "%.0f\n", huge}'`
EOF
 
Old 04-10-2014, 11:30 PM   #4
kbp
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Registered: Aug 2009
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Not contributing to the exact question but here's some custom puppet facts I put together that may be useful:
Code:
# pagesize.rb
require 'facter'
Facter.add(:pagesize) do
  setcode do
     Facter::Util::Resolution.exec('getconf PAGE_SIZE')
  end
end
Code:
# physpages.rb
require 'facter'
Facter.add(:physpages) do
  setcode do
     Facter::Util::Resolution.exec('getconf _PHYS_PAGES')
  end
end
Code:
# recshmall.rb
# generates recommended value for SHMALL based on %80 of pysical memory
require 'facter'
Facter.add(:recshmall) do
  setcode do
    physpgs = Facter.value(:physpages)
    if physpgs
      recshmall = Integer(physpgs) / 10 * 8
    end
    recshmall
  end
end
Then we just use:
Code:
kernel.shmall = <%= @recshmall %>
.. in our /etc/sysctl.conf template
 
  


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