🚀 go-pugleaf

In article <27BD8836.5548@orion.oac.uci.edu> iglesias@orion.oac.uci.edu (Mike Iglesias) writes:

   Can someone tell me what the "requests for clusters denied" means in
   netstat -m output?

There are two types of mbufs. One is a small character array which
tends to be used for character-oriented networking traffic and
networking data structures (sockaddrs and protocol control blocks)
inside the kernel. The other type of mbuf is the cluster. This points
at a page of kernel virtual memory and it tends to be used for bulk
networking traffic, typically file transfers.

If the system cannot allocate a cluster mbuf when one is required, it
increments a counter. It is the value of this counter that gets
displayed by netstat. Reasons for this vary. It may be that the mbuf
pool is empty. This should be rare - it should only happen when
there's a kernel bug that causes mbufs not to be freed when they are
no longer needed. [The mbuf pool can also be exhausted if there are
extremely high amounts of networking activity going on - i.e. many
thousands of active sockets in use.] If the mbuf pool is OK, a cluster
request can be denied because either the kernel cannot assign a page
table entry to it or allocate a page of physical memory to that page
table entry. Again, these should be rare events.

The most common reason will be that the mbuf pool is too small. In
short, there aren't enough mbufs to go round. This can be fixed by
reconfiguring the kernel to increase the size of the pool, just like
you'd increase the size of the file table or proc table if the system
was complaining that these tables were filled. The kernel cannot
complain about mbuf requests failing as the requests may be made at
interrupt time when it is not reasonable to print things on the system
console. 

		Jim