For a week now one of our clients websites have had very poor performance.
It seem that the application pool was recycle all the time.
We have tried everything until I notices this setting
<setting name="Caching.DisableCacheSizeLimits" value="false" />
We’re running a 64-bit application where this is not needed, since it has a larger memory space available.
Flipping this switch seems to have solved the problem.