Ruslan - FreeBSD Quarterly Status Report - Q2 2019

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Hello, Allan and Benedict!

Thanks for your great show!  I have a question for you.

I recently read ``FreeBSD Quarterly Status Report - Second Quarter
2019''[1] and didn't understand a part of the ``BIO_DELETE support for
the swap pager'' section.  The latter says that "as of r349286 in
-CURRENT ... swapon(8) can send BIO_DELETE to all blocks on the
specified device immediately prior to configuring it as a swap device".

I had installed my FreeBSD 13.0-CURRENT amd64 before r349286 (I used
r349251 snapshot[2]), and now I run r351728.  When I was installing my
system, I created a volume (ZVOL) for swap using:

# zfs create -V 12288M -o org.freebsd:swap=on -o checksum=off zroot/swap

(zroot is a pool on NVMe drive)

then rebooted to the just installed FreeBSD, and I got working (I
believe) swap:

$ swapctl -l
Device:       1024-blocks     Used:
/dev/zvol/zroot/swap  12582912         0

I neither changed /etc/rc.d/zfs script (and its `zfs_start_main`
function), nor used swapon(8) to enable swapping on that ZVOL.

And my question is: does my swap "device" support/receive BIO_DELETE/ATA
TRIM command?  After all, I didn't issued `swapon -E ...`, I just
specified the user-defined option `org.freebsd:swap` for the ZVOL.

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