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List:       freebsd-fs
Subject:    Re: misc/151111: vnodes leakage during zfs unmount
From:       Gleb Kurtsou <gleb.kurtsou () gmail ! com>
Date:       2010-10-19 14:47:33
Message-ID: 20101019144733.GA2672 () tops
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On (19/10/2010 17:36), Gleb Kurtsou wrote:
> On (18/10/2010 12:30), Gleb Smirnoff wrote:
> > The following reply was made to PR kern/151111; it has been noted by GNATS.
> > 
> > From: Gleb Smirnoff <glebius@FreeBSD.org>
> > To: "Oleg A. Mamontov" <oleg@mamontov.net>
> > Cc: kib@FreeBSD.org, pjd@FreeBSD.org, freebsd-gnats-submit@FreeBSD.org
> > Subject: Re: misc/151111: vnodes leakage during zfs unmount
> > Date: Mon, 18 Oct 2010 16:11:55 +0400
> > 
> > On Thu, Sep 30, 2010 at 11:56:18AM +0000, Oleg A. Mamontov wrote:
> > O> for i in `jot 1000`; do zfs mount tank; printf '%4d   ' $i; sysctl \
> > vfs.numvnodes; zfs umount tank; done O> ########################
> > O>  1   vfs.numvnodes: 708
> > O>  2   vfs.numvnodes: 709
> > O>  3   vfs.numvnodes: 710
> > O>  4   vfs.numvnodes: 711
> > O>  5   vfs.numvnodes: 712
> > O> 
> > O> ..
> > O> 
> > O> 995   vfs.numvnodes: 1702
> > O> 996   vfs.numvnodes: 1703
> > O> 997   vfs.numvnodes: 1704
> > O> 998   vfs.numvnodes: 1705
> > O> 999   vfs.numvnodes: 1706
> > O> 1000   vfs.numvnodes: 1707
> 
> In my tests zfs vnodes are getting properly gc'ed. Most likely maxvnodes
> limit is not hit during the test, thus vnodes are not reclaimed.
> 
> Try making all available vnodes used, e.g. by running
> 'find /usr >/dev/null' before the test. Running the test you'll see
> vfs.numvnodes going up and down.
> 
> It's more visible after lowering kern.maxvnodes. I've used
> kern.maxvnodes=1000. Default value on my system is ~127000.
Please ignore my previous email. There is indeed a leak.

> > Here is my lame investigation of the problem. In the zfs_domount() function
> > we've got the following code:
> > 
> > /* Grab extra reference. */
> > VERIFY(VFS_ROOT(vfsp, LK_EXCLUSIVE, &vp) == 0);
> > VOP_UNLOCK(vp, 0);
> > 
> > I suppose this code is expected to put an extra reference on the
> > vfsp->mnt_vnodecovered vnode. Do I mistake here? If I don't then this is
> > the source of leak.
> > 
> > Debugging shows that zfs_zget(), called subsequently from zfs_root(),
> > does not find an existing znode/vnode and allocates a new one, see at the
> > end of zfs_zget() function. This vnode gots a reference and is forgotten.
> > 
> > Sorry, if I am being mistaken :)
> > 
> > -- 
> > Totus tuus, Glebius.
> > _______________________________________________
> > freebsd-fs@freebsd.org mailing list
> > http://lists.freebsd.org/mailman/listinfo/freebsd-fs
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