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Date: Fri, 3 May 2019 23:14:19 +0300
From: Konstantin Belousov <kostikbel@gmail.com>
To: Garrett Wollman <wollman@csail.mit.edu>
Cc: freebsd-net@freebsd.org
Subject: Re: Disabling 9k jumbo clusters on mce(4)
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On Fri, May 03, 2019 at 03:37:11PM -0400, Garrett Wollman wrote:
> <<On Fri, 3 May 2019 20:47:15 +0300, Konstantin Belousov <kostikbel@gmail.com> said:
> 
> > On Fri, May 03, 2019 at 12:55:54PM -0400, Garrett Wollman wrote:
> >> Does anyone have an easy patch to keep mce(4) from trying to use 9k
> >> jumbo mbuf clusters?  I think I went down this road once before but
> >> the fix wasn't as obvious as it is for the Intel drivers.  (I assume
> >> the hardware is not so broken that it requires packets to be stored in
> >> contiguous physical memory.)
> > mce(4) only uses 9k clusters when you configured jumbo size larger than 4k.
> > See r336407.
> 
> Yes, and the point is to make it not use them *ever*, no matter what
> the MTU is.  9k clusters are Bad News; given the choice I would just
> as soon rip out all the code for greater-than-page-size clusters, but
> that would be way more divergence-from-upstream in my source tree than
> I can reasonably manage.

In fact I was wrong, I forgot that code, sorry. It does not use clusters
at all, instead the revision I mentioned loads a chain of mbufs of the
MCLBYTES size for receive. Jumbo size only defines the number of mbufs.