Comment by vlovich123

glibc is not written in a containerized environment and I personally think it’s telling that a core feature of the more recent tcmalloc Google open sourced is that it returns memory efficiently, so clearly even in containerized environments it’s important. The reason for this is how kernels deal with compressing pages and pages released to the kernel are explicitly zeroed (unlike the user space allocator) which aids in the efficiency of the compression even in a containerized workload because those pages can just be skipped since they’re unused and the kernel can share the reference zeroed page for lazy allocations.

Also the kernel itself has memory needs for lots of things and it not having memory or having to go on a hunt to find contiguous pages is not good. Additionally in a VM or container environment there’s other containers and VMs running on that machine so the memory will also eventually get percolated up to the hyper visor to rebalance. None of this happens if the user space allocator hangs on to memory needlessly in a greedy fashion and indeed such an application would be more subject to the OOM killer.