memory fragmentation issues in 1.2?

Paul T pault12345 at
Wed Dec 6 22:56:14 UTC 2006

--- George Schlossnagle <george at> wrote:

> Paul T wrote:
> > Turn off the OOM killer and see what happens?
> I could.  I would expect it to actually OOM and die
> when it exceeds
> addressable memory space.

All I'm saying is that it could be that OOM gets
nervous too early. If I would post you the cacti
pictures from my servers you would see than the amount
of 'free RAM' goes down for a while. And then at some
point Linux re-claims it. It's OK behaviour.

> > 
> > If you are running Linux, you might be surprised
> with
> > the behaviour of it's memory manager on memcached
> node
> > dedicated to memcached.
> To be clear, I'm not seeing a performance issue, as
> I'm not actively
> swapping (even when my RSS exceeds phys mem), I'm
> seeing a loss of
> addressable memory issue, which is both generally
> troubling and
> eventually terminal.

Are you complaining about the amount of 'free RAM'
going down on Linux? If that is what you call
'addressabe RAM' - I see no reason to be troubled.

> Memory fragmentation isn't a myth.  I can create you
> an app quite easily
> that does not leak memory but will eventually run
> out of addressable
> memory space and eventually fail in malloc.  

Please do. I will run it on my build of Linux and tell
you the results.

You know that implementations of malloc are not casted
in stone and the fact that you can bring down one
malloc implementation only proves the weakness of
particular malloc implementation, right?

> I'm
> happy for that not to
> be the case here, but that behavior is certainly
> realizable (and I've
> seen it and had to work around it in large
> commercial server
> applications as well - so it's not academic either).

When was that? 
A lot have changed in Linux codebase in last 10 years.


> George

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