Re: KSM For All Via LD_PRELOAD?

[Jes Sorensen <Jes.Sorensen@redhat.com>]

On 06/10/10 11:09, Gordan Bobic wrote:
> On 06/10/2010 08:44 AM, Jes Sorensen wrote:
>> Not sure if it is worth it, but you might want to look at ElectricFence
>> which does malloc wrapping in a somewhat similar way. It might save you
>> some code :)
> 
> I'll look into it, but I don't see this requiring more than maybe 50
> lines of code, including comments, headers and Makefile. I was planning
> to literally just intercept mmap()/brk()/malloc() and mark them with
> madvise() when the underlying call returns.

I suspect it will grow in complexity to catch corner cases, but see
where it takes you.

> Which brings me to another question:
> 
> Would intercepting malloc() be completely redundant if mmap() is
> intercepted? Would I also need to do something with intercepting free()?
> Is three anything else I would need to intercept?

You need to have a look at glibc to see what it is doing. I am not sure
what the current malloc implementation is based on these days.

>> Whether or not you will run into problems if you run it system wise is
>> really hard to predict. Any other application that might be linked in a
>> special way or use preload itself might bark, but you can try it out and
>> see what explodes.
> 
> Thanks for the heads up. Can you think of any such applications off the
> top of your head?

Sorry, nothing off hand. A normal Linux distro runs so many applications
just at bootup that it's very hard to keep track of what might cause
problems. You might end up having to create a blacklist in your library
to work around it, but you will only find out when you start trying the
boot.

Cheers,
Jes