Date: Tue, 16 Mar 2021 11:27:39 -0600 From: Alan Somers <asomers@freebsd.org> To: freebsd-fs <freebsd-fs@freebsd.org> Subject: Understanding the vfs.nfsd.request_space* sysctls Message-ID: <CAOtMX2geF7Tv7VYc9WtK23a%2BnDzJzD2ehVKp94=xANjTA9S9Tg@mail.gmail.com>
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Could somebody help me understand the meaning of the various vfs.nfsd.request_space* sysctls, and what implication they have for tuning NFS? I have several NFS servers. Most are performing well, but one with a metadata-heavy workload (NFS 4.1, no delegations, lots of Sequence, GetAttr and Lookup ops) is not. Total throughput is a not-unreasonable several hundred MB/s, but some clients are limited to very slow speeds, sometimes writing at < 10 MB/s. The request_space sysctls show some pretty stark divergence between the well-performing and poor-performing servers: sysctl well-performing poor-performing request_space_used < 6 M varies, but currently 40 M request_space_used_highest < 39 M 24 G request_space_throttle_count 0 35 So what does request_space_used measure, anyway? And how can I either increase the available space or decrease the stuff that's using it? -Alan
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