Managing cache memory in a network element based on costs associated with fetching missing cache entries

1. A network element, comprising:

a data structure, configured to store multiple rules specifying processing of packets received from a communication network;

a cache memory, configured to cache multiple rules comprising a subset of the rules stored in the data structure, wherein each rule that is cached in the cache memory has a respective cost value that is a function of an actual number of memory-access operations required to perform a lookup operation of the respective rule in the data structure; and

circuitry, configured to:

receive one or more packets from the communication network;

process the received packets in accordance with one or more of the rules, by retrieving the rules from the cache memory when available, or by performing a lookup operation in the data structure otherwise;

select a rule to be evicted from the cache memory, based on one or more respective cost values of the rules currently cached; and

evict the selected rule.

2. The network element according to claim 1 , wherein the circuitry is configured to retrieve a rule from the data structure, to cache the retrieved rule in the cache memory, and to store a respective cost value in association with the rule cached.

3. The network element according to claim 1 , wherein the cost value comprises two or more cost levels corresponding to a quantized version of the actual number of memory-access operations.

4. The network element according to claim 1 , wherein the cost value of a given rule comprises a latency incurred in retrieving the given rule from the data structure.

5. The network element according to claim 1 , wherein the circuitry is configured to select from the cache memory multiple candidate rules for which the respective cost values fall within a predefined range of cost values, and to select the rule to be evicted from among the candidate rules.

6. The network element according to claim 1 , wherein the circuitry is configured to select from the cache memory multiple candidate rules, independently of the cost values, and to select the rule to be evicted, from among the candidate rules, based on the respective cost values of the candidate rules.

7. The network element according to claim 1 , wherein the circuitry is configured to select the rule to be evicted randomly, with a predefined probability.

8. The network element according to claim 1 , wherein the circuitry is configured to assign to the rules currently cached respective eviction attributes, to select from the cache memory multiple candidate rules based on the assigned eviction attributes, to calculate for the candidate rules respective combined costs as a function of the respective cost values and eviction attributes, and to select the rule to be evicted based on the combined costs.

9. The network element according to claim 1 , wherein the circuitry is configured to estimate the cost of retrieving a given rule from the data structure, and to determine the respective cost value based on the estimated cost.

10. A method, comprising:

in a network element, storing in a data structure multiple rules specifying processing of packets received from a communication network;

caching in a cache memory multiple rules comprising a subset of the rules stored in the data structure, wherein each rule that is cached in the cache memory has a respective cost value that is a function of an actual number of memory-access operations required to perform a lookup operation of the respective rule in the data structure;

receiving one or more packets from the communication network, and processing the received packets in accordance with one or more of the rules, by retrieving the rules from the cache memory when available, or by performing a lookup operation in the data structure otherwise;

selecting a rule to be evicted from the cache memory, based on one or more respective cost values of the rules currently cached; and

evicting the selected rule.

11. The method according to claim 10 , and comprising retrieving a rule from the data structure, caching the retrieved rule in the cache memory, and storing a respective cost value in association with the rule cached.

12. The method according to claim 10 , wherein the cost value comprises two or more cost levels corresponding to a quantized version of the actual number of memory-access operations.

13. The method according to claim 10 , wherein the cost value of a given rule comprises a latency incurred in retrieving the given rule from the data structure.

14. The method according to claim 10 , wherein selecting the rule to be evicted comprises selecting from the cache memory multiple candidate rules for which the respective cost values fall within a predefined range of cost values, and selecting the rule to be evicted from among the candidate rules.

15. The method according to claim 10 , wherein selecting the rule to be evicted comprises selecting from the cache memory multiple candidate rules, independently of the cost values, and selecting the rule to be evicted, from among the candidate rules, based on the respective cost values of the candidate rules.

16. The method according to claim 10 , wherein selecting the rule to be evicted comprises selecting the rule to be evicted randomly, with a predefined probability.

17. The method according to claim 10 , and comprising assigning to the rules currently cached respective eviction attributes, wherein selecting the rule to be evicted comprises selecting from the cache memory multiple candidate rules based on the assigned eviction attributes, calculating for the candidate rules respective combined costs as a function of the respective cost values and eviction attributes, and selecting the rule to be evicted based on the combined costs.

18. The method according to claim 10 , and comprising estimating the cost of retrieving a given rule from the data structure, and determining the respective cost value based on the estimated cost.