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From: richard bader <richard@bader-muenchen.de>
Subject: disk space not freed when deleting files in null_mounted filesystem
Message-ID: <2e11d942-0856-7ce4-56ef-3774046f8df8@bader-muenchen.de>
Date: Thu, 9 Jun 2016 12:13:08 +0200
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Hello,

i've a filesystem mounted with mount_nullfs.
When i delete a large file in this filesystem, the space on the disk is 
not freed.
The space becomes freed when i unmount the filesystem.


to reproduce this:

root@main2:/tmp # mkdir lnk src
root@main2:/tmp # mount_nullfs src lnk
root@main2:/tmp # mount | grep lnk
/tmp/src on /tmp/lnk (nullfs, local)
root@main2:/tmp # df -h .
Filesystem     Size    Used   Avail Capacity  Mounted on
/dev/ada0p2     58G     40G     13G    75%    /
root@main2:/tmp # dd if=/dev/zero of=lnk/foo bs=1G count=3
3+0 records in
3+0 records out
3221225472 bytes transferred in 7.856793 secs (409992411 bytes/sec)
root@main2:/tmp # df -h .
Filesystem     Size    Used   Avail Capacity  Mounted on
/dev/ada0p2     58G     43G     10G    80%    /
root@main2:/tmp # rm lnk/foo
root@main2:/tmp # df -h .
Filesystem     Size    Used   Avail Capacity  Mounted on
/dev/ada0p2     58G     43G     10G    80%    /
root@main2:/tmp # umount /tmp/lnk
root@main2:/tmp # df -h .
Filesystem     Size    Used   Avail Capacity  Mounted on
/dev/ada0p2     58G     40G     13G    75%    /


my system:

root@main2:/tmp # uname -a
FreeBSD main2.bader.loc 10.2-RELEASE-p18 FreeBSD 10.2-RELEASE-p18 #8 
r301112: Wed Jun  1 11:08:24 CEST 2016 
root@main2.bader.loc:/usr/obj/usr/src/sys/MYKERNEL  amd64

are the any options for mount_nullfs ?

best regards

richard