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Date: Sun, 20 Jul 2014 11:56:38 -0400 (EDT)
From: Garrett Wollman <wollman@hergotha.csail.mit.edu>
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To: jhb@freebsd.org
Subject: Re: NFS client READ performance on -current
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In article <201407151034.54681.jhb@freebsd.org>, jhb@freebsd.org writes:

>Hmm, I am surprised by the m_pullup() behavior that it doesn't just
>notice that the first mbuf with a cluster has the desired data already
>and returns without doing anything.

The specification of m_pullup() is that it returns a *writable* mbuf
(and thus also that the "length" provided is less than MHLEN).
Clusters are read-only.

-GAWollman