Date: Fri, 12 Dec 2014 10:33:59 -0500 From: John Baldwin <jhb@freebsd.org> To: Mike Gelfand <Mike.Gelfand@logicnow.com> Cc: Konstantin Belousov <kostikbel@gmail.com>, "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org> Subject: Re: [BUG] Getting path to program binary sometimes fails Message-ID: <3715296.8JkIjC2VMR@ralph.baldwin.cx> In-Reply-To: <27C465FC-E8C7-44CB-A812-65213BB8AC9F@logicnow.com> References: <91809230-5E81-4A6E-BFD6-BE8815A06BB2@logicnow.com> <2066750.N3TZpYSHCy@ralph.baldwin.cx> <27C465FC-E8C7-44CB-A812-65213BB8AC9F@logicnow.com>
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On Friday, December 05, 2014 03:52:41 PM Mike Gelfand wrote:
> On Dec 5, 2014, at 6:19 PM, John Baldwin <jhb@freebsd.org> wrote:
> >> No, not NFS but ZFS. Could that be an issue? The FreeBSD 8 machine I
> >> mentioned before has UFS.
> >>
> >> Also, as you can see from the video I recorded (and from the code I
> >> provided), path resolution succeeds and fails within fractions of a
> >> second
> >> after process startup.
> >
> > Are you seeing vnodes being actively recycled? In particular, do you see
> > vfs.numvnodes close to kern.maxvnodes? You can try raising
> > kern.maxvnodes.
> > If vfs.numvnodes grows up to the limit then as long as you can stomach the
> > RAM of having more vnodes around that would increase the changes of your
> > paths remaining valid.
>
> When the call works, sysctl returns:
> vfs.numvnodes: 59638
> kern.maxvnodes: 204723
> The times it doesn't, the output is:
> vfs.numvnodes: 60017
> kern.maxvnodes: 204723
> I've selected maximum numbers. Monitoring was made with
> while sysctl vfs.numvnodes kern.maxvnodes; do sleep 0.1; done
>
> So it seems that's not related, correct? 60K is much less than 200K.
Yes. Unfortunately, we don't expose a raw counter for vnode recycling (I
should really add one). I think we might also purge unused vnodes if we have
too many "free" vnodes. However, directories that aren't currently open by
a process (meaning via opendir()) count as "unused", so are subject to
purging. You can try increasing "vfs.wantfreevnodes".
Also, please try this patch. It just adds a counter for recycled vnodes. If
this value increases during your test then it does show that recycling is
occurring. If it doesn't, then that rules it out.
Index: vfs_subr.c
===================================================================
--- vfs_subr.c (revision 275512)
+++ vfs_subr.c (working copy)
@@ -156,6 +156,10 @@ static int vlru_allow_cache_src;
SYSCTL_INT(_vfs, OID_AUTO, vlru_allow_cache_src, CTLFLAG_RW,
&vlru_allow_cache_src, 0, "Allow vlru to reclaim source vnode");
+static u_long recycles_count;
+SYSCTL_ULONG(_vfs, OID_AUTO, recycles, CTLFLAG_RW, &recycles_count, 0,
+ "Number of vnodes recycled");
+
/*
* Various variables used for debugging the new implementation of
* reassignbuf().
@@ -988,6 +992,7 @@ vtryrecycle(struct vnode *vp)
__func__, vp);
return (EBUSY);
}
+ atomic_add_long(&recycles_count, 1);
if ((vp->v_iflag & VI_DOOMED) == 0)
vgonel(vp);
VOP_UNLOCK(vp, LK_INTERLOCK);
--
John Baldwin
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