I have this strange problem with the CLR memory usage.

Now I have 2 .NET applications where the CLR at least wants a lot of memory,
they actually do about the same thing so with the same load they both should
need the same amount of memory. When working simultaneously they compete for
the available memory on the machine and everything seems fine, the total
memory usage on the machine is close to the physical memory limit.

But then one of the applications takes a dive in memory usage, collecting a
lot of unused object in the higher generations and after that it doesn't seem
to want to allocate more memory. The machine now has a lot of available
memory and the performance of the application with lower memory usage seems
to suffer in performance because of the lack of available memory (seems it
the word, it performs worse then the other one but I'm not really sure it's
because of the low
memory usage, the memory usage is however uncharacteristicly low). Why won't
it allocate more memory when there's a lot of free memory on the machine?

Anyone noticed something like this and has a clue on why the CLR behaives
this way? I'm guessing that the CLR for some reason doesn't think it benefits
from allocating more memory all the sudden but why would this be?