Re: Free memory pages estimation for process use

[matthew sporleder <msporleder%gmail.com@localhost>]

On Thu, Jul 26, 2012 at 2:59 PM, Nicolas Joly <njoly%pasteur.fr@localhost> 
wrote:
>
> Hi,
>
> While testing free memory consumable requests with OGS (Open Grid
> Scheduler), i noticed that free memory reported by a NetBSD host was
> amazingly low ... preventing its use.
>
> By example, on a 8GB NetBSD/amd64 machine running -current :
>
> njoly@lanfeust [gridscheduler/source]> qhost
> HOSTNAME                ARCH         NCPU  LOAD  MEMTOT  MEMUSE  SWAPTO  
> SWAPUS
> -------------------------------------------------------------------------------
> lanfeust.sis.pasteur.fr nbsd-x86_64     8  0.09    7.8G    7.7G   40.0G     
> 0.0
>
> At the same time 'vmstat -s'report the following:
>
>      4096 bytes per page
>         8 page colors
>   2032144 pages managed
>     10496 pages free
>   1247833 pages active
>    616160 pages inactive
>         0 pages paging
>      1510 pages wired
>      8937 zero pages
>         1 reserve pagedaemon pages
>        40 reserve kernel pages
>     10717 anonymous pages
>   1848644 cached file pages
>      6142 cached executable pages
> [...]
>
> Looking into the OGS code i found that memory/swap values are fetched
> with VM_UVMEXP2 sysctl :
>
>   mib[0] = CTL_VM;
>   mib[1] = SGE_VM_UVMEXP;
>   size   = sizeof(uvmexp);
>
>   sysctl(mib, sizeof(mib)/sizeof(int), &uvmexp, &size, NULL, 0);
>
>   /* Memory */
>   mem_info->mem_total = ((double) uvmexp.npages * uvmexp.pagesize) / (1024 * 
> 1024);
>   mem_info->mem_free  = ((double) uvmexp.free   * uvmexp.pagesize) / (1024 * 
> 1024);
>
>   /* Swap */
>   mem_info->swap_total = ((double) uvmexp.swpages * uvmexp.pagesize) / (1024 
> * 1024);
>   mem_info->swap_free = (((double) uvmexp.swpages - uvmexp.swpginuse) * 
> uvmexp.pagesize) / (1024 * 1024);
>
> But mem_free does only take uvmexp.free member into account, which
> seems wrong to me. At least uvmexp.inactive should be added ...
>
> Is it correct ? Anything else i missed ?
>
> Thanks in advance,
> Regards.
>
> --
> Nicolas Joly
>
> Biology IT Center
> Institut Pasteur, Paris.

I look at free memory like this:
https://github.com/msporleder/cons/blob/master/free/free.c
but it looks like you're going the same thing.

Doesn't linux have the same problem where file caching takes away from
total "free" space?