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Date:      Sun, 27 Aug 2000 22:50:11 +0100
From:      David Malone <dwmalone@maths.tcd.ie>
To:        Archie Cobbs <archie@whistle.com>
Cc:        freebsd-net@freebsd.org, freebsd-current@freebsd.org
Subject:   Re: Proposal to clarify mbuf handling rules
Message-ID:  <20000827225011.A10714@lanczos.maths.tcd.ie>
In-Reply-To: <200008272125.OAA66159@bubba.whistle.com>; from archie@whistle.com on Sun, Aug 27, 2000 at 02:25:55PM -0700
References:  <200008272125.OAA66159@bubba.whistle.com>

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On Sun, Aug 27, 2000 at 02:25:55PM -0700, Archie Cobbs wrote:

> What do people think? If this is generally agreeable I'll try to
> work on putting together a patch set for review.

Myself and Ian Dowse have been talking about almost this issue
recently in relation to sbcompress. At the moment sbcompress is
too conservative about compressing mbuf chains, with the result
that it is easily possible to run many machines out of mbuf clusters.

(We've seen this problem with netscape and kioslave).

At the moment sbcompress only compresses into mbufs, where it could
also compress into clusters, providing they have a reference count
of 1. However, this still means it can't compress into jumbo buffers
associated with gigabit ethernet and the like.

We were thinking it might be a good idea to have a flag associated
with mbufs which means they are writable, providing the reference
count is 1. Then we can provide a macro for checking writability.
This flag could be set on jumbo ethernet buffers, but not sendfile
buffers (for example).

	David.


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