Dentry negativity
Dentry negativity
Posted Mar 17, 2020 20:25 UTC (Tue) by nix (subscriber, #2304)In reply to: Dentry negativity by willy
Parent article: Dentry negativity
> The primary difficulty here is deciding how many negative dentries to allow. How to detect thrashing (a signal to increase the number of dentries allowed) and how to detect underutilisation of the cache (an opportunity to shrink the dcache and give the memory back).
Just track the hit rate, hits versus misses versus additions for lookups across the entire cache? If there are many more additions than hits, shrink the cache; if there are many more misses than hits, grow it. (Or something like that.)
(Downside: this sort of global counter is a cache nightmare, but the figures need only be approximate, so the usual trick of having per-CPU counters occasionally spilled into a global counter should work fine.)