Why can a process get Out of Memory even if the memory shows free?

The process can encounter an Out of Memory (OOM) error even if the system memory shows as free, for several reasons:

1. Process or container level restrictions — for example, cgroups or Docker may limit the available memory for the process.
2. Memory fragmentation — free memory exists but is scattered in small blocks, and the process cannot allocate a large contiguous block.
3. Language or runtime limits — in Go, for example, there may be a limit on the maximum heap or stack size.
4. Address space — 32-bit processes are limited in the amount of addressable memory, even if physical memory is larger.

Example: if a Go program runs in a container with a 512MB limit and tries to allocate more than the limit, an OOM will occur, even if there is free memory on the host.