Rob Norris d323fbf49c FreeBSD: zfs_putpages: don't undirty pages until after write completes
In syncing mode, zfs_putpages() would put the entire range of pages onto
the ZIL, then return VM_PAGER_OK for each page to the kernel. However,
an associated zil_commit() or txg sync had not happened at this point,
so the write may not actually be on disk.

So, we rework that case to use a ZIL commit callback, and do the
post-write work of undirtying the page and signaling completion there.
We return VM_PAGER_PEND to the kernel instead so it knows that we will
take care of it.

The original version of this (238eab7dc1) copied the Linux model and did
the cleanup in a ZIL callback for both async and sync. This was a
mistake, as FreeBSD does not have a separate "busy for writeback" flag
like Linux which keeps the page usable. The full sbusy flag locks the
entire page out until the itx callback fires, which for async is after
txg sync, which could be literal seconds in the future.

For the async case, the data is already on the DMU and the in-memory
ZIL, which is sufficient for async writeback, so the old method of
logging it without a callback, undirtying the page and returning is more
than sufficient and reclaims that lost performance.

Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Mark Johnston <markj@FreeBSD.org>
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
Closes #17533
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OpenZFS is an advanced file system and volume manager which was originally developed for Solaris and is now maintained by the OpenZFS community. This repository contains the code for running OpenZFS on Linux and FreeBSD.

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Official Resources

Installation

Full documentation for installing OpenZFS on your favorite operating system can be found at the Getting Started Page.

Contribute & Develop

We have a separate document with contribution guidelines.

We have a Code of Conduct.

Release

OpenZFS is released under a CDDL license. For more details see the NOTICE, LICENSE and COPYRIGHT files; UCRL-CODE-235197

Supported Kernels

  • The META file contains the officially recognized supported Linux kernel versions.
  • Supported FreeBSD versions are any supported branches and releases starting from 13.0-RELEASE.
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