CoMeT is a low-cost RowHammer mitigation mechanism that uses Count-Min Sketch (CMS) to track DRAM row activations and prevent RowHammer bitflips with minimal area, performance, and energy overhead. The key idea is to use hash-based counters to track DRAM row activations, which allows for efficient and secure prevention of RowHammer bitflips. CoMeT consists of two main components: the Counter Table (CT) and the Recent Aggressor Table (RAT). CT tracks DRAM row activation counts with low area overhead using hash-based counters, while RAT tracks recently identified aggressor rows with per-row counters. CoMeT prevents unnecessary preventive refreshes by using CT and RAT together, ensuring that only necessary rows are refreshed. CoMeT is evaluated across a diverse set of workloads and shows significant improvements in performance and energy efficiency compared to existing RowHammer mitigation mechanisms. CoMeT achieves a low area overhead and performs well at very low RowHammer thresholds, making it an effective solution for mitigating RowHammer in DRAM-based systems.CoMeT is a low-cost RowHammer mitigation mechanism that uses Count-Min Sketch (CMS) to track DRAM row activations and prevent RowHammer bitflips with minimal area, performance, and energy overhead. The key idea is to use hash-based counters to track DRAM row activations, which allows for efficient and secure prevention of RowHammer bitflips. CoMeT consists of two main components: the Counter Table (CT) and the Recent Aggressor Table (RAT). CT tracks DRAM row activation counts with low area overhead using hash-based counters, while RAT tracks recently identified aggressor rows with per-row counters. CoMeT prevents unnecessary preventive refreshes by using CT and RAT together, ensuring that only necessary rows are refreshed. CoMeT is evaluated across a diverse set of workloads and shows significant improvements in performance and energy efficiency compared to existing RowHammer mitigation mechanisms. CoMeT achieves a low area overhead and performs well at very low RowHammer thresholds, making it an effective solution for mitigating RowHammer in DRAM-based systems.