git: 8f8e975c79 - main - Status/2025Q2/packrat.adoc: Add report

The branch main has been updated by salvadore:

URL: https://cgit.FreeBSD.org/doc/commit/?id=8f8e975c798a328e9b7985bce6e812c6a3193e01

commit 8f8e975c798a328e9b7985bce6e812c6a3193e01
Author:     Rick Macklem <rmacklem@FreeBSD.org>
AuthorDate: 2025-06-24 09:50:39 +0000
Commit:     Lorenzo Salvadore <salvadore@FreeBSD.org>
CommitDate: 2025-06-24 09:51:49 +0000

    Status/2025Q2/packrat.adoc: Add report
    
    Reviewed by:    status (Pau Amma <pauamma@gundo.com>)
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+=== Packrat - NFS client caching on non-volatile storage
+
+Contact: Rick Macklem <rmacklem@freebsd.org>
+
+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 agressively 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 agressively 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 makes doing this more feasible.
+
+The patch is getting stable now, but I am not sure if it will be ready for inclusion in FreeBSD 15 as an experimental feature enabled via a new mount option called "packrat".
+
+The main thing I still need to do is code a writeback kernel thread.
+Right now, dirty chunks stored on client local non-volatile storage get written back to the NFSv4.1/4.2 server upon umount.
+This can result in the umount taking a long time (as in many minutes).
+To alleviate this, I am planning on implementing a writeback kernel process that will walk the non-volatile storage and write the dirty chunks back.
+The trick is to make it aggressive enough that most dirty chunks have been written back when a umount is done, but not so aggressive that it impedes the performance of synchronous NFSv4.1/4.2 RPCs.
+
+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.