From owner-freebsd-hackers  Tue Apr 20 14: 0:14 1999
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To: Matthew Dillon <dillon@apollo.backplane.com>
Cc: John Dyson <dyson@iquest.net>, hackers@FreeBSD.ORG
Subject: Re: Directories not VMIO cached at all! 
In-reply-to: Your message of "Tue, 20 Apr 1999 12:28:26 PDT."
             <199904201928.MAA99383@apollo.backplane.com> 
From: David Greenman <dg@root.com>
Reply-To: dg@root.com
Date: Tue, 20 Apr 1999 13:56:32 -0700
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>    All right.  Then what about this.... right now vm_page_t's are
>    required to be PAGE_SIZE'd.
>
>    We change this.  We allow vm_page_t's to be sized in multiples of
>    DEV_BSIZE from 0 through to PAGE_SIZE, but not crossing a physical
>    page boundry.  We get rid of vm_page_t->valid and vm_page_t->dirty and
>    turn those into PG_VALID and PG_DIRTY flags.  we add vm_page_t->size.

   I prefer the current architecture, actually. Several problems come to
mind with your proposed scheme: On for example is problems with handling
filesystems with block sizes less than a page. I think there are a lot of
other problems, too, but I'm too busy to go looking for them. I don't
really see how it fixes anything, either - the wastage for directory blocks
will still be there unless you create fictitious pages and/or support offsets
within a page (in which case you likely will have page aliasing problems
to deal with). Yuck.

-DG

David Greenman
Co-founder/Principal Architect, The FreeBSD Project - http://www.freebsd.org
Creator of high-performance Internet servers - http://www.terasolutions.com


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