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NFSv4 "Courteous Server" Lands As Part Of Linux 5.19 NFSD Changes
NFSv4 Courteous Server functionality is for not immediately expunging the state on lease expiration but continuing to recognize previously-generated state tokens until there are any conflicts with requests from another client or the NFSD server is rebooted.
Chuck Lever III of Oracle explains in the NFSD pull request from Thursday, "We introduce "courteous server" in this release. Previously NFSD would purge open and lock state for an unresponsive client after one lease period (typically 90 seconds). Now, after one lease period, another client can open and lock those files and the unresponsive client's lease is purged; otherwise if the unresponsive client's open and lock state is uncontended, the server retains that open and lock state for up to 24 hours, allowing the client's workload to resume after a lengthy network partition."
The NFSD updates for Linux 5.19 also address a long-standing issue with NFSv4 file creation to make internal failures and race conditions less likely to yield unwanted file creation. There is also a fault injector added, preparations for PREEMPT_RT, and fixes.
More details on the NFSD changes for Linux 5.19 via this pull request.