[CentOS] XFS and CentOS 4.3

Aleksandar Milivojevic alex at milivojevic.org
Thu Aug 17 14:08:41 UTC 2006


Quoting Daniel de Kok <danieldk at pobox.com>:

> On Wed, 2006-08-16 at 16:08 -0500, Aleksandar Milivojevic wrote:
>> Hmmm...  Any downside to setting it to 0?
>
> Yeah. It disables the OOM killer, possibly leading to the situation
> where no one can allocate memory. Having it enabled (and set to one
> process) will try to pick a process according to the least surprise
> principle.

So, does "no one can allocate memory" means:

a) things will be put on hold until kswapd frees enough pages (if  
possible, than apps will start dying), or
b) the machine will freeze

The (a) is what usually happens on other operating system (Tru64  
and/or Solaris).  And it is acceptable.  If backing store is  
overallocated, and free swap falls to zero, kernel kills userland  
process that it can't handle anymore.  However, as I said many times  
in this thread, this is not what happened in my case.  I had more than  
enough free space on swap to accomodate offending application.

>> Node 0 Normal: 0*4kB 0*8kB 0*16kB 0*32kB 0*64kB 0*128kB 0*256kB
>> 0*512kB 0*1024kB 0*2048kB 0*4096kB = 0kB
>> Node 0 HighMem: empty
>
> Seems like a very bad OOM situation. Remember that the swapper is not
> just an extension of physical memory, since kswapd has to take care of
> paging out memory pages. If you are allocating huge chunks of memory in
> a short time, you may want to crank up the vm.min_free_kbytes tunable.
> This variable sets the low watermark of free memory, and setting it
> higher gives the kernel more room for emergency allocations (e.g.
> letting kswapd do its work). Setting it to 4096KB should help a lot,
> though I have seen people setting it much higher on servers.

In my case, min_free_kbytes was set to 1015 (default, I guess).  I'll  
try crancking it up.  Machine has 1 gig of memory, so there's plenty  
of space to play with that parameter before performance will suffer  
noticably.  Anyhow, I'd expect that min_free_kbytes would be  
performance tunable.  Not something I'd need to touch to make machine  
more stable.

-- 
NOTICE: If you are not intended recipient, you are hereby notified
that by reading this message you agreed not to disturb frogs during
mating season.  For more info, visit http://www.8-P.ca/




More information about the CentOS mailing list