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Date: Tue, 6 Feb 2001 21:25:03 +0100
From: Christoph Hellwig <hch@ns.caldera.de>
To: Linus Torvalds <torvalds@transmeta.com>
Cc: Ben LaHaise <bcrl@redhat.com>, Ingo Molnar <mingo@elte.hu>,
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Subject: Re: [Kiobuf-io-devel] RFC: Kernel mechanism: Compound event wait
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In-Reply-To: <Pine.LNX.4.10.10102061121530.1474-100000@penguin.transmeta.com>; from torvalds@transmeta.com on Tue, Feb 06, 2001 at 11:32:43AM -0800
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On Tue, Feb 06, 2001 at 11:32:43AM -0800, Linus Torvalds wrote:
> Traditionally, a "bh" is only _used_ for small areas, but that's not a
> "bh" issue, that's a memory management issue. The code should pretty much
> handle the issue of a single 64kB bh pretty much as-is, but nothing
> creates them: the VM layer only creates bh's in sizes ranging from 512
> bytes to a single page.
> 
> The IO layer could do more, but there has yet to be anybody who needed
> more (becase once you hit a page-size, you tend to get into
> scatter-gather, so you want to have one bh per area - and let the
> low-level IO level handle the actual merging etc).

Yes.  That's one disadvantage blown away.

The second is that bh's are two things:

 - a cacheing object
 - an io buffer

This is not really an clean appropeach, and I would really like to
get away from it.

	Christoph

-- 
Whip me.  Beat me.  Make me maintain AIX.
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