Memory Hierarchy

Which pair correctly states the main advantage and drawback of using large pages (huge pages)?

  1. AAdvantage: lower cache miss rate. Drawback: more TLB misses
  2. BAdvantage: page faults disappear. Drawback: more disk space is used
  3. CAdvantage: fewer TLB misses. Drawback: more internal fragmentation
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Answer: C. Advantage: fewer TLB misses. Drawback: more internal fragmentation

Larger pages let one TLB entry translate a wide range, sharply reducing TLB misses for programs with large data. On the other hand, even small amounts of data are allocated in large page units, increasing unused space (internal fragmentation) and making allocation less flexible. TLB misses decrease rather than increase, and the cache miss rate does not depend directly on page size. Page faults do not disappear either.

  • A. TLB misses actually decrease, and the cache miss rate is not directly affected.
  • B. Page faults do not disappear.
  • C. Correct. TLB misses fall, but internal fragmentation grows.
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More Memory Hierarchy questions

  1. When each row of a 2D array is 4,096 bytes (a power of two), walking down a column can cause many misses even though the cache has spare capacity. Which countermeasure is effective?
  2. Roughly how many times longer is a main-memory DRAM access than an L1 cache hit (for typical PC or server CPUs)?
  3. What is the role of the valid bit attached to each cache line?
  4. What is the main effect of a victim cache, a small fully associative buffer that temporarily holds lines evicted from the L1 cache?
  5. In a multilevel cache with an L2 below the L1, what is the L2's main role?