During one 10-minute run of a heavy mixed workload a period of several seconds of very low throughput was seen:

• During the pause all statistics appear to be consistent with a large number of cache evictions, resulting in a lot of writes, system cpu time, and context switches. This heavy eviction load seems like a plausible cause for the low throughput during this period.
• Immediately before the pause the number of bytes in the cache jumped by about 4 GiB between two samples about 0.1 seconds apart. This is a plausible trigger for the heavy eviction load.
• During the pause bytes and pages in cache declined slowly, presumably a result of the page evictions.
• The pause ends with a sudden drop in the size of the cache by about 4 GiB between two samples about 0.1 seconds apart.

Here are the specific samples

• just before increase
  "localTime":"2015-01-15T18:42:20.344Z"
  "bytes currently in the cache":4315898330
  "pages currently held in the cache":60756

• just after increase
  "localTime":"2015-01-15T18:42:20.472Z"
  "bytes currently in the cache":8594367123
  "pages currently held in the cache":60598

• just before decrease
  "localTime":"2015-01-15T18:42:25.058Z"
  "bytes currently in the cache":7242022268
  "pages currently held in the cache":35169

• just after decrease
  "localTime":"2015-01-15T18:42:25.170Z"
  "bytes currently in the cache":2941126278
  "pages currently held in the cache":35137

The size of the sudden jump was: 7242022268 - 2941126278 = 3.98 GiB

The size of the sudden drop was: 8594367123 - 4315898330 = 4.01 GiB

Neither a sudden increase nor a sudden decrease of cache size by 4 GiB in 0.1 seconds due to real cached data is plausible.