https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=238670
Bug ID: 238670
Summary: [libkvm][patch] kvm_getswapinfo() returns swap device
sizes too small incorrectly
Product: Base System
Version: 12.0-RELEASE
Hardware: Any
OS: Any
Status: New
Severity: Affects Only Me
Priority: ---
Component: bin
Assignee: b...@freebsd.org
Reporter: o...@j.email.ne.jp
kvm_getswapinfo() function returns smaller device sizes than the actual swap
device sizes configured available. "systat -swap" uses this API and shows
problem. "sysctl -c" uses a different API and displays correct sizes.
While "usesd" swap device sizes are reported correctly, when a swap device is
used fully, it looks like system haven overwritten next partition.
The root of problem is libkvm subtracts vm.dmmax, maximum VOP I/O allowed, form
size of device erroneously.
The following shows that 1 MB swap device is prepared, attached, and then fully
used. Given FreeBSD swap skips 2 4k blocks, 1016 is the correct size available
for swapping.
# dd if=/dev/zero of=1MB bs=1M count=1
1+0 records in
1+0 records out
1048576 bytes transferred in 0.035823 secs (29271150 bytes/sec)
# mdconfig -a -t vnode -f 1MB
md0
# swapon /dev/md0
# swapctl -l
Device: 1024-blocks Used:
/dev/ada0s1b 2097144 0
/dev/md0 1016 0
# mount -t tmpfs tmpfs /mnt/tmp
# dd if=/dev/zero of=/mnt/tmp/fill bs=1M count=2000
2000+0 records in
2000+0 records out
2097152000 bytes transferred in 36.267636 secs (57824337 bytes/sec)
# swapctl -l
Device: 1024-blocks Used:
/dev/ada0s1b 2097144 144220
/dev/md0 1016 1016
# systat -swap
Disk 1K-blocks Used /0% /10 /20 /30 /40 /50 /60 /70 /80 /90 /100
ada0s1b 2097016 144216 XXXX
md0 888 1016
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XX 2097904 145232 XXXX
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