On Fri, May 18, 2012 at 10:39 AM, Les Mikesell <lesmikesell at gmail.com>wrote: > On Fri, May 18, 2012 at 11:24 AM, Michael Coffman > <michael.coffman at avagotech.com> wrote: > > > >> If you are already overcommitted, what do you expect to happen when > >> you say not to allow that? The kernel doesn't have a really good way > >> to handle that situation (or any other OOM condition for that > >> matter...). > >> > >> > > OK. So I was confused because free shows I have plenty of memory and I > am > > only now noticing that Committed_AS shows a very large value. This is > > largely an idle system: > > > > total used free shared buffers cached > > Mem: 2052176 951648 1100528 0 147580 626096 > > -/+ buffers/cache: 177972 1874204 > > Swap: 2052088 0 2052088 > > > > So my real question should have been why would the Committed_AS value be > so > > large? > > Committed_AS: 137197248820 kB > > > > On the exact same hardware with fresh build of centos5u4 and overcommit > > turned on: > > Committed_AS: 125716 kB > > I think that means an application has malloc()'d but not actually used > a huge amount of memory. It used to be a common practice to test the > amount of memory available by requesting more until the request > failed, so it could be meaningless. If overcommit is turned off the > app gets an error when it expects and backs off. The Committed_AS is > an estimate of how much RAM/swap you would be likely to need if the > requested storage is actually used. > > I get how overcommit works and it's affect on malloc. I intentionally turn it off so malloc will return a correct value when a process can't get enough memory. What I currently don't understand is the large value of Committed_AS on my centos6/rhel6 systems. I just did a fresh build of centos6u2 and there is very little running and the value is: Committed_AS: 136382202700 kB There is almost nothing running.... Filtering out kernel processes here is the list of running processes I tried to post the ps listing, both as inline text and as an attached ps.txt file and the message was rejected by Symantec :( -- > Les Mikesell > lesmikesell at gmail.com > _______________________________________________ > CentOS mailing list > CentOS at centos.org > http://lists.centos.org/mailman/listinfo/centos > -- -MichaelC