Linux Server Kernel Same-page Merging for Memory Overcommit

Episode 127 of Linux Server Admin with Fexingo dives into Kernel Same-page Merging (KSM) – a Linux kernel feature that deduplicates identical memory pages to reduce RAM usage in virtualized and containerized environments. Lucas and Luna walk through how KSM works under the hood, from the memory scan daemon to the merge_across_nodes and sleep_millisecs tuning knobs. They discuss real-world use cases at scale, including a case study of a 40 percent memory saving on a VM host running 200 Ubuntu guests. The hosts explain when KSM pays off (dense virtual desktops, lab clusters) and when it hurts (latency-sensitive databases). They also cover security considerations like side-channel risks and the madvise MADV_MERGEABLE flag. Practical commands for enabling, monitoring, and disabling KSM are included, along with a note on alternatives like zswap and zram. Perfect for sysadmins managing memory-constrained Linux servers.

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