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Date: Sat, 8 Dec 2001 02:54:46 +0100
From: Jens Axboe <axboe@suse.de>
To: Marvin Justice <mjustice@austin.rr.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>, linux-kernel@vger.kernel.org
Subject: Re: highmem question
Message-ID: <20011208015446.GC32569@suse.de>
In-Reply-To: <Pine.LNX.4.30.0112071404280.29154-100000@mustard.heime.net> <01120719300102.00764@bozo> <3C116CC6.2030808@zytor.com> <01120719534703.00764@bozo>
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On Fri, Dec 07 2001, Marvin Justice wrote:
> > There is no way of fixing it.
> 
> All I know is that a streaming io app I was playing with showed a drastic 
> performance hit when the kernel was compiled with CONFIG_HIGHMEM. On W2K we 
> saw no slowdown with 2 or even 4GB of RAM so I think solutions must exist.

That's because of highmem page bouncing when doing I/O. There is indeed
a solution for this -- 2.5 or 2.4 + block-highmem-all patches will
happily do I/O directly to any page in your system as long as your
hardware supports it. I'm sure we're beating w2k with that enabled :-)

-- 
Jens Axboe

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