Date: 17 Oct 2001 04:23:15 +0200 From: Dag-Erling Smorgrav <des@ofug.org> To: John Baldwin <jhb@FreeBSD.org> Cc: dillon@freebsd.org, hackers@freebsd.org Subject: Re: Some questions regarding vfs / ffs Message-ID: <xzpk7xvvwbw.fsf@flood.ping.uio.no> In-Reply-To: <XFMail.011016191649.jhb@FreeBSD.org> References: <XFMail.011016191649.jhb@FreeBSD.org>
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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 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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