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To: "Albert D. Cahalan" <acahalan@cs.uml.edu>
Cc: alan@lxorguk.ukuu.org.uk (Alan Cox), linux-kernel@vger.kernel.org
Subject: Re: bigphysarea support in 2.2.19 and 2.4.0 kernels
In-Reply-To: <200012222311.eBMNBgr459298@saturn.cs.uml.edu>
From: Jes Sorensen <jes@linuxcare.com>
Date: 23 Dec 2000 21:11:20 +0100
In-Reply-To: "Albert D. Cahalan"'s message of "Fri, 22 Dec 2000 18:11:42 -0500 (EST)"
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>>>>> "Albert" == Albert D Cahalan <acahalan@cs.uml.edu> writes:

>> bigmem is 'last resort' stuff. I'd much rather it is as now a
>> seperate allocator so you actually have to sit and think and decide
>> to give up on kmalloc/vmalloc/better algorithms and only use it
>> when the hardware sucks

Albert> It isn't just for sucky hardware. It is for performance too.

Albert> 1. Linux isn't known for cache coloring ability. Even if it
Albert> was, users want to take advantage of large pages or BAT
Albert> registers to reduce TLB miss costs. (that is, mapping such
Albert> areas into a process is needed... never mind security for now)

Albert> 2. Programming a DMA controller with multiple addresses isn't
Albert> as fast as programming it with one.

LOL

Consider that allocating the larger block of memory is going to take a
lot longer than it will take for the DMA engine to read the
scatter/gather table entries and fetch a new address word now and
then.

Jes
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