Date: Tue, 5 Jan 1999 15:08:57 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: Terry Lambert <tlambert@primenet.com> Cc: dyson@iquest.net, tlambert@primenet.com, pfgiffun@bachue.usc.unal.edu.co, freebsd-hackers@FreeBSD.ORG Subject: Re: questions/problems with vm_fault() in Stable Message-ID: <199901052308.PAA98255@apollo.backplane.com> References: <199901051847.LAA10199@usr02.primenet.com>
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:> had historically been split between VFS and VM, and the interfaces were
:> defined without both parties understanding the needs. Since that is
:> understood now, things should be reworked.
:
:Hmmm.
:
:I don't really buy this for the general case, which I believe is
:still stacking layers that don't access local media.
:
:For local media FS's, things which actially do I/O through a page
:fault, this is probably correct.
Ouch.. no, get away from the 'local media' concept - it's a big time
bust. If you make the distinction between hard media and soft media
(or local media verses remote media), all you do is screw up the layering
model. Even now, traditional hard-media-backed VFS layers such as UFS
can be stacked on top of soft media layers such as MFS, which in turn
is stacked on top of SWAP (which may be a hard or soft media layer
itself). If you throw NFS into the fray it gets worse. It just doesn't
work. Also, these sorts of schemes require both interacting VFS layers
to have knowledge about each other that goes far beyond what two
layers ought to know about each other.
-Matt
: Terry Lambert
: terry@lambert.org
:---
Matthew Dillon Engineering, HiWay Technologies, Inc. & BEST Internet
Communications & God knows what else.
<dillon@backplane.com> (Please include original email in any response)
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