vm info from a hung system

[John Baldwin]

On Friday, September 14, 2012 1:32:43 am Vijay Singh wrote:
> Need some expert help. I have a system that is hung hard, and I was
> able to get it into gdb. From show_vmstat I see:
> 
> (kgdb-amd64-7.4-95) show_vmstat
> SYSTEM MEMORY INFORMATION:
> mem_wire:         285970432 (    272MB) Wired: disabled for paging out
> mem_active:  +    400105472 (    381MB) Active: recently referenced
> mem_inactive:+     56840192 (     54MB) Inactive: recently not referenced
> mem_cache:   +            0 (      0MB) Cached: almost avail. for allocation
> mem_free:    +            0 (      0MB) Free: fully available for allocation
> mem_gap_vm:  +       753664 (      0MB) Memory gap: vm
> -------------- ------------ ----------- ------
> mem_all:     =    743669760 (    709MB) Total real memory managed
> mem_gap_sys: +     22765568 (     21MB) Memory gap: system
> -------------- ------------ -----------
> mem_phys:    =    766435328 (    730MB) Total phys memory
> -------------- ------------ -----------
> 
> SYSTEM MEMORY SUMMARY:
> mem_used:         709595136 (    676MB)      Used memory
> mem_avail:   +     56840192 (     54MB) Available memory
> -------------- ------------ ----------- ------
> mem_total:   =    766435328 (    730MB)     Total memory
> 
> What is this telling me?

Oof.  I think we generally don't cope with not having any
free memory at all (mem_cache + mem_free).  That is, I imagine
the system was unable to make forward progress, possibly it
had to malloc() something (GEOM is terrible for doing this)
while trying to page out something to free up space.  I would
look at the state of the pagedaemon kthread to see why it isn't
able to run.

-- 
John Baldwin