Which of the following tools are used to measure memory usage? (Select THREE correct answers.)

`mpstat` is primarily used to report processor-related statistics, particularly for multi-processor systems, not memory usage.

`pstree` displays running processes as a tree, showing process relationships, not resource utilization like memory.

`sar` (System Activity Reporter) provides comprehensive system statistics, including memory usage (e.g., `sar -r` for memory and swap space).

`top` displays a real-time summary of system usage, including detailed information about memory (total, free, used, buffers, cache) and individual process memory consumption.

`vmstat` (virtual memory statistics) reports on processes, memory, paging, block IO, traps, and CPU activity, with specific columns dedicated to virtual and physical memory usage.