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Allow disabling of unmapped I/O on FreeBSD

Description

Allow disabling of unmapped I/O on FreeBSD

We have a tunable which permits one to disable the use of unmapped I/O
for the buffer cache. Respect it in ZFS as well. This is useful for
KMSAN, which cannot easily maintain shadow state for unmapped pages.

No functional change intended, as unmapped I/O is permitted by default
and there's no real reason to disable it in practice except for
debugging.

Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Tony Nguyen <tony.nguyen@delphix.com>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: Mark Johnston <markj@FreeBSD.org>
Closes #12446

Details

Provenance
markjAuthored on Aug 2 2021, 7:18 PM
GitHub <noreply@github.com>Committed on Aug 2 2021, 7:18 PM
Parents
rG7eebcd2be6ac: Avoid small buffer copying on write
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