git: f390100c60 - main - Status/2023Q4/packrat.adoc: Add report

The branch main has been updated by salvadore:

URL: https://cgit.FreeBSD.org/doc/commit/?id=f390100c60f00e1c8b7d759aa9e2e1315742b78e

commit f390100c60f00e1c8b7d759aa9e2e1315742b78e
Author:     Rick Macklem <[email protected]>
AuthorDate: 2024-01-04 16:35:40 +0000
Commit:     Lorenzo Salvadore <[email protected]>
CommitDate: 2024-01-04 16:35:40 +0000

    Status/2023Q4/packrat.adoc: Add report
    
    Reviewed by:    status (Pau Amma <[email protected]>)
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 .../en/status/report-2023-10-2023-12/packrat.adoc  | 63 ++++++++++++++++++++++
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+=== Packrat - NFS client caching on non-volatile storage
+
+Contact: Rick Macklem <[email protected]>
+
+NFSv4.1/4.2 provides support for a feature called delegations.
+When a NFSv4.1/4.2 client holds a delegation, the client has certain rights to a file, including a guarantee that no other client will make changes to the file unless the delegation is recalled.
+As such, when a client holds a delegation for a file, it can aggressively cache the file's data, knowing that it will not be modified by other clients until it returns the delegation.
+
+This project is intended to allow the NFSv4.1/4.2 client to aggressively cache file data on client local non-volatile storage, when the client holds a delegation for the file.
+I created a patch long ago to try and do this for NFSv4.0, but it was never at a stage where it was worth using.
+This project is a complete rewrite of the patch, done in part because NFSv4.1/4.2 plus other recent NFSv4-related changes make doing this more feasible.
+
+I now have code running fairly well and hope to have a patch ready for others to test this winter.
+Early testing shows promise.
+For a test run of "make buildkernel", the test with and without packrat enabled performed as follows:
+
+.NFS operation counts
+[cols="1,1,1,1,1,1", frame="none", options="header"]
+|===
+| NFS operation counts
+| Getattr
+| Lookup
+| Read
+| Write
+| Total RPCs
+
+|with packrats
+|433506
+|99254
+|0
+|0
+|371736
+
+|without packrats
+|2359913
+|97954
+|10748
+|0
+|2318810
+
+|===
+
+.Elapsed Run Time
+[cols="1,1,1", frame="none", options="header"]
+|===
+| Elapsed Run Time (sec)
+| with packrat
+| without packrat
+
+| 
+|5561
+|6203
+
+|===
+
+As you can see, the packrat case ran a little faster and with fewer RPCs.
+Although this test was run on my little LAN, it is hoped that a NFSv4.1/4.2 mount over a WAN would show a larger difference in performance.
+I will note that the packrat cache was primed by unrolling a tarball of FreeBSD's [.filename]#/usr/src# into the NFSv4.1/4.2 mount.
+
+This will be very much an experimental feature, but it is hoped it will allow NFS mounts to be used more effectively, particularily in WAN situations, such as a mobile laptop.
+
+There is still work to be done, particularily with respect to recovery of delegations after a NFSv4.1/4.2 client restart.
+Hopefully, the next status report will include a URL that allows downloading of a patch for user testing.