in the mbuf header.
* Use the new cached paddr feature of the pool_cache API to record
the physical address of mbuf clusters. (We cannot use a ctor for
clusters, since clusters have no constructed form; they are merely
buffers).
Bus_dma back-ends may use the cached physical addresses to save having to
extract the physical address from virtual.
* Provide space in m_ext recording the vm_page *'s for an SOSEND_LOAN_CHUNK-
sized non-cluster external buffer. Use this in the sosend_loan code to
save having to extract the physical address from virtual and then look
up the vm_page *'s.
* Provide an indication that an external buffer is mapped read-only at
the MMU. Set this flag for the external buffer in the sosend_loan
case, since loaned pages are always mapped read-only. Bus_dma back-ends
may use this information to save cache flushing, since a cache flush of
a read-only mapping is redundant on some architectures (the cache would
have already been flushed when making the mapping read-only).
Part 2 in a series of simple patches contributed by Wasabi Systems
to improve network performance.
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