Date: Tue, 16 Oct 2001 19:29:51 -0700 (PDT) From: Matthew Dillon <dillon@apollo.backplane.com> To: Dag-Erling Smorgrav <des@ofug.org> Cc: John Baldwin <jhb@FreeBSD.ORG>, hackers@FreeBSD.ORG Subject: Re: Some questions regarding vfs / ffs Message-ID: <200110170229.f9H2Tph84237@apollo.backplane.com> References: <XFMail.011016191649.jhb@FreeBSD.org> <xzpk7xvvwbw.fsf@flood.ping.uio.no>
next in thread | previous in thread | raw e-mail | index | archive | help
:
:John Baldwin <jhb@FreeBSD.org> writes:
:> Not quite. You see, when we set the mount vnode pointer inside the
:> vnode, we get the mntvnode mutex while holding the vnode interlock,
:> so the order is thus vnode -> mntvnode. So, the ffs_sync() loop
:> can't lock the vnode while holding the mntvnode lock. It actually
:> used to do that.
:
:You're basically agreeing with me :) ffs_sync() releases the mntvnode
:lock early so it can grab the vnode lock, but if I'm right about it
:not needing the vnode lock yet at that point, it can gold the mntvnode
:lock longer - until after it's decided whether or not the vnode needs
:syncing - which means one less mntnode lock release / acquisition and
:one less vnode lock acquisition / release per non-dirty vnode,
:reducing the number of lock operations per vnode from four to nearly
:zero (as the ratio of dirty vnodes to clean vnodes is usually very
:low, the average number of lock operations per vnode examined will
:approach zero)
:
:DES
:--
:Dag-Erling Smorgrav - des@ofug.org
This would be an improvement, but not enough of an improvement. We need
to be able to discard most of the vnodes while simply holding the mntvnode
mutex, without even having to get the vnode mutex or release the mntvnode
mutex. When we find a vnode that 'might' require some action, that's
when we do the heavy-weight mutex junk. At least in the case
where it's ok to occassionally not get it right (which is most cases).
-Matt
To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-hackers" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?200110170229.f9H2Tph84237>