How does the OOM Killer choose a process to kill? How is oom_score calculated?

The OOM Killer in Linux selects a process to kill based on an assessment of how 'guilty' the process is of causing memory shortage. It uses the oom_score parameter, which is calculated by the kernel.

oom_score depends on several factors:

• Memory used by the process (RSS, swap).
• The lifetime of the process (the longer, the lower the priority for killing).
• The process priority (for example, processes with higher priority or with the oom_score_adj flag lower are less likely to be killed).

The higher the oom_score, the more likely the process will be chosen for termination.

The oom_score_adj parameter allows manual adjustment of the score, setting a value from -1000 (never kill) to +1000 (most likely to kill).

Thus, the OOM Killer selects the process with the highest score, considering memory, priority, and settings, to minimize system damage when freeing memory.