Date: Sun, 13 Sep 1998 01:29:06 -0700 From: David Greenman <dg@root.com> To: Don Lewis <Don.Lewis@tsc.tdk.com> Cc: freebsd-fs@FreeBSD.ORG Subject: Re: vm system interaction with nullfs Message-ID: <199809130829.BAA19667@implode.root.com> In-Reply-To: Your message of "Sun, 13 Sep 1998 00:01:42 PDT." <199809130701.AAA22846@salsa.gv.tsc.tdk.com>
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> >Since the vm system keeps track of what it has in memory by (vnode, offset), >how is this supposed to work when stackable filesystems are in use which >create multiple vnodes for a single filesytem object, or is this broken? >Unless this works right, it looks like you'll end up with multiple copies >of the same disk blocks in memory and in memory copies may all be different. > >It would seem that in the case of nullfs and similar transparent filesytems, >the vm system should always use the lowest vnode, but this doesn't seem to >be implemented (though I could just be getting lost in the maze of twisty >little passages). It's even messier if the layer isn't transparent, >like an encryption layer. Yes, that's the fundamental reason why nullfs is broken. It's been known for years that the solution is to always reference the same underlying VM object, but noone has yet gotten around to implementing that correctly. -DG David Greenman Co-founder/Principal Architect, The FreeBSD Project To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-fs" in the body of the message
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