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Date:      Wed, 18 Apr 2001 20:53:18 +0200
From:      Poul-Henning Kamp <phk@critter.freebsd.dk>
To:        Matt Dillon <dillon@earth.backplane.com>
Cc:        Julian Elischer <julian@elischer.org>, Robert Watson <rwatson@FreeBSD.ORG>, Kirk McKusick <mckusick@mckusick.com>, Rik van Riel <riel@conectiva.com.br>, freebsd-hackers@FreeBSD.ORG, David Xu <bsddiy@21cn.com>
Subject:   Re: vm balance 
Message-ID:  <42362.987619998@critter>
In-Reply-To: Your message of "Wed, 18 Apr 2001 11:11:19 PDT." <200104181811.f3IIBJp25644@earth.backplane.com> 

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In message <200104181811.f3IIBJp25644@earth.backplane.com>, Matt Dillon writes:

>    Actually, all this talk does imply that VM objects should be independant
>    of vnodes.  Devices may need to mmap (requiring a VM object), but 
>    don't need all the baggage of a vnode.  Julian is absolutely correct 
>    there.

Well, you have other VM Objects which doesn't map to vnodes:  swap
backed anonymous objects for instance.

>    We do need to guarentee locking order, which means that all I/O
>    operations should be consistent.  If a device or vnode is mmap()able,
>    then all read, write, and truncation(/extention) ops *should* run
>    through the VM object first:

We guarantee that today my mapping the actual hardware and my having
all read/writes be synchronouse.   I remember at least one other
UNIX which didn't make that guarantee.

--
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

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