On 2022-Feb-02 11:49:44 +0200, Andriy Gapon <a...@freebsd.org> wrote: >On 02/02/2022 11:14, Warner Losh wrote: >> On Wed, Feb 2, 2022 at 2:05 AM Andriy Gapon <a...@freebsd.org >> <mailto:a...@freebsd.org>> wrote: >> Hmm... it looks like both the old and new (Open)ZFS use BIO_FLUSH command >> without BIO_ORDERED flag. Not sure if it happens to do the right thing >> anyway >> or not. >> >> >> It's an unordered flush then. The flush will happen whenever. I have a vague >> memory that ZFS will only issue this command in cases where there's no other >> I/O >> pending. > >I think that there is still a potential problem that an earlier write request >might get re-ordered after the flush. >I think that we should add BIO_ORDERED for correctness.
I've raised https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=261731 to make geom_gate support BIO_ORDERED. Exposing the BIO_ORDERED flag to userland is quite easy (once a decision is made as to how to do that). Enhancing the geom_gate clients to correctly implement BIO_ORDERED is somewhat harder. I've done some experiments and OpenZFS doesn't generate BIO_ORDERED operations so I've also raised https://github.com/openzfs/zfs/issues/13065 I haven't looked into how difficult that would be to fix. -- Peter Jeremy
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