Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!thunder.mcrcim.mcgill.edu!snorkelwacker.mit.edu!usc!wuarchive!uunet!mcsun!ukc!strath-cs!baird!jim From: jim@cs.strath.ac.uk (Jim Reid) Newsgroups: comp.sys.sequent Subject: Re: network clusters Message-ID: Date: 19 Feb 91 16:36:39 GMT References: <27BD8836.5548@orion.oac.uci.edu> Sender: jim@cs.strath.ac.uk Organization: Computer Science Dept., Strathclyde Univ., Glasgow, Scotland. Lines: 34 In-reply-to: iglesias@orion.oac.uci.edu's message of 16 Feb 91 19:29:58 GMT 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