From owner-freebsd-arch  Mon Feb  5  9:52:53 2001
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Date: Mon, 5 Feb 2001 09:52:20 -0800 (PST)
From: Matthew Jacob <mjacob@feral.com>
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To: Matt Dillon <dillon@earth.backplane.com>
Cc: Randell Jesup <rjesup@wgate.com>,
	"Justin T. Gibbs" <gibbs@scsiguy.com>,
	Mike Smith <msmith@FreeBSD.ORG>, Dag-Erling Smorgrav <des@ofug.org>,
	Dan Nelson <dnelson@emsphone.com>,
	Seigo Tanimura <tanimura@r.dl.itc.u-tokyo.ac.jp>, arch@FreeBSD.ORG
Subject: Re: Bumping up {MAX,DFLT}*PHYS (was Re: Bumping up {MAX,DFL}*SIZ in
 i386)
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>     The funny thing about all of this is that we go to great pains to
>     make things contiguous in KVM, but the bus dma code has to then break
>     things up into page-by-page DMAs anyway.  I'd much rather just hand the
>     I/O subsystem a list of vm_page_t's without bothering to map them into
>     KVM.

See solaris && SunOS for this one. Also, the busdma code doesn't 'have' to
break things up. If the underlying physical pages are contiguous then there's
no need to have multiple entries.

You should note, btw, that not all archictures require or can use
scatter-gather (sparc, for instance, which has an iommu).



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