svn commit: r248196 - head/sys/nfs

[Gleb Smirnoff]

  Okay,

  I will redo my patch to make default not to allow > PAGE_SIZE
clusters.

On Tue, Mar 12, 2013 at 10:19:05PM +0100, Andre Oppermann wrote:
A> Jumbos always were physically contiguous.  That was the very reason for
A> their existence.  They were invented to allow early NIC's with limited
A> DMA capabilities to handle jumbo ethernet frames.  Today they should only
A> be used for DMA challenged NIC's and nothing else.

They definitely were not physically contigous prior to r174247.

A> > Let me repeat: there is a lot of code, that does handmade allocation of
A> > an mbuf chain of an arbitrary length using mbufs and common clusters. This
A> > code can be cut and use m_getm2(), if we can restrict it to avoid page size
A> > clusters. I don't have time to dig deeper in the code and analyze and test
A> > whether it can support page sized clusters in chains.
A> 
A> m_getm2() can be used in any such case and doesn't have to avoid PAGE_SIZE
A> clusters.  PAGE_SIZE jumbo clusters are fine.  Larger than PAGE_SIZE is not.
A> 
A> When the code is able to work with mbuf chains the exact size of each cluster
A> isn't important anymore.  We can use the optimal size.

Do you volunteer to fix if anything is broken? If not, I'd prefer to
be conservative and make m_getm() capable to produce chains without
clusters bigger than MCLBYTES.

-- 
Totus tuus, Glebius.