Talk Around Town: A Dev Says Caching inode-to-Policy Mappings Cut eBPF Kernel CPU Cost by ~90%

What Folks Are Hollering About

Well, butter my biscuit and call it a breakthrough — a developer named Nathan Naveen published a blog post on September 11, 2026, over at nathannaveen.dev, claiming that one slick caching trick yanked roughly 90% of the kernel CPU cost right out of their eBPF-based Linux security agent.

According to the author, the priciest chore in their agent wasn't the actual allow-or-deny enforcement — it was figuring out which doggone policy applied to a given file open in the first place, which involved reconstructing filesystem paths and climbing up parent dentries like a coonhound treed by every single event.

The author says they fixed this by caching which policy applies to each inode — a technique they call memoization — so that repeatedly accessed files, like a database hammering the same paths over and over, don't force the system to redo that dentry-walk climb every single time.

The author also says they have since open-sourced the code at github.com/bomfather/agent, though no independent party found in search results has yet reviewed or cited that repository.

What We Actually Know for Sure

eBPF LSM hooks are a real and established Linux kernel mechanism — the official kernel documentation confirms they allow privileged users to implement system-wide mandatory access control and audit policies without touching kernel source code, which is handier than a pocket on a shirt.

Independent sources, including ADHDecode's 2026 analysis of eBPF performance overhead, confirm that repeated or excessive eBPF map lookups are a well-documented source of overhead, with one source noting that map operations can become the dominant factor in CPU consumption — so the general problem Naveen describes is not invented.

The path-versus-inode tension is also real and documented: according to Aqua Security and the Aegis-BPF project, path-based enforcement rules are considered detection-grade because pathname-to-inode resolution is vulnerable to TOCTOU race conditions, while inode-based rules are prevention-grade but can be invalidated by filesystem events like renames or overwrites.

What Nobody Has Checked Yet

Here's where the pig gets stuck in the fence: that headline-grabbing ~90% CPU reduction figure comes entirely from Naveen's own measurement of Naveen's own project, and no independent benchmark, peer-reviewed study, or named third-party reviewer has been found that evaluates this specific optimization.

The Hacker News discussion, while providing community commentary and some technical color, does not independently validate the performance numbers — folks talking at the barn ain't the same as somebody actually counting the chickens.

Real-world results are expected to vary substantially depending on workload, file-access patterns, policy set size, and kernel version, so treating the author's figure as a generalizable benchmark would be like judging all fishing holes by the one catfish you caught last Tuesday.

The Neighbors Are Squabbling Over the Framing

Over on Hacker News, at least one commenter pushed back on how the contribution is being pitched, saying they would have titled the piece something like 'Calculating cache keys for filesystem paths in eBPF,' because that — rather than memoization as a general concept — is the genuinely interesting problem that got solved here.

That reframing matters, because memoization is about as new as cornbread: the clever part, if the commenter is right, is navigating the gnarly limitations of eBPF and Linux filesystem semantics to derive a cache key that actually holds up, not the act of caching itself.

The inode-based caching approach also inherits the prevention-grade tradeoffs described above — filesystem events like file overwrites or renames can invalidate cached mappings, a complication the author's blog post must address, and one that adds real-world messiness to any tidy efficiency narrative.

Our Analysis: Neat Trick, But Hold Your Horses

This is analysis, not reporting: the underlying systems-programming insight — stop redoing expensive dentry walks for files you've already seen — is genuinely sensible and lines up with well-understood eBPF performance principles, even if the novelty is disputed.

Also as analysis: if the numbers hold up under scrutiny from independent engineers, a 90% kernel CPU reduction in a security agent would be the kind of result worth pinning to the workshop wall — but right now the tape measure belongs to the same fella who built the shelf.

The broader eBPF performance research landscape is legitimately active — independent sources note that production deployments at large companies have achieved meaningful CPU reductions through eBPF optimization — but none of that context validates this specific project's claimed figures.

Bottom line as analysis: Naveen's post is a worthwhile read for systems programmers wrestling with eBPF overhead, but the ~90% claim deserves independent reproduction before anyone hangs their hat on it as settled engineering gospel.