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Daniel
Asked: 2012-09-25 07:17:36 +0800 CST

Find out how many memory my server would need ideally?

  • 772

I have a pretty busy GNU/Linux server that I think needs more RAM. I know that the free command doesn't show the amount of RAM that is used.

So I was stumbling upon Commited_As in /proc/meminfo. It currently shows 57972 kB which isn't much. Is this the amount of RAM that the processes use "right now" or is this an estimate of how many additional RAM it would take to never run out of memory with this load?

linux

2 Answers

  1. Best Answer

    Yeah, Committed_AS is the field to look for. What Robert said, it is a 99.99% guarantee that the system will not OOM if all the memory requests are granted and allocated by that kernel at that particular instant.

    From kernel source.

    Committed_AS: The amount of memory presently allocated on the system.
    714 The committed memory is a sum of all of the memory which
    715 has been allocated by processes, even if it has not been
    716 "used" by them as of yet. A process which malloc()'s 1G
    717 of memory, but only touches 300M of it will only show up
    718 as using 300M of memory even if it has the address space
    719 allocated for the entire 1G. This 1G is memory which has
    720 been "committed" to by the VM and can be used at any time
    721 by the allocating application. With strict overcommit
    722 enabled on the system (mode 2 in 'vm.overcommit_memory'),
    723 allocations which would exceed the CommitLimit (detailed
    724 above) will not be permitted. This is useful if one needs
    725 to guarantee that processes will not fail due to lack of
    726 memory once that memory has been successfully allocated.

    It is declared as a struct in source and is used in the function _vm_enough_memory() to see whether a process can grow in memory or not.

    To cut short, it is a pretty good parameter to watch for memory issues.

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  2. Committed_As is an estimate of how much RAM you would need to make a 99.99% guarantee that there never is OOM.

    That said I'm not sure how accurate this is or if I'd bet the farm on it. On my current server it's almost twice my active + inactive memory usage while on another server i have it shows 61mb while the server has about a gig in active. Kinda raises my suspicions about this number...

    http://www.redhat.com/advice/tips/meminfo.html

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