Re: mbuf usage for an idle machine

From: Mike Silbersack (silby_at_silby.com)
Date: 08/27/03

  • Next message: Garrett Wollman: "Re: mbuf usage for an idle machine" 
    Date: Wed, 27 Aug 2003 11:40:17 -0500 (CDT)
To: "Giovanni P. Tirloni" <gpt@tirloni.org>

    On Wed, 27 Aug 2003, Giovanni P. Tirloni wrote:

    > Hi,
    >
    > I've been reading about mbufs and how they're used for
    > holding network packets and socket buffers and the
    > output of 'netstat -m' for a idle machine I've here
    > made me curious about how FreeBSD handles it in -CURRENT.
    >
    > Why is it using so many mbufs when it's idle? My
    > small kwnowledge doesn't permit me to answer this
    > question yet ;)

    The mbufs in question are (mostly) being used as receive buffers by the
    network drivers. With modern DMA based cards, you pre-allocate the
    buffers, then hand them over to the card's control. Once they're filled
    with packet data, the NIC informs the OS, which replaces them with new
    buffers.

    A lot of our drivers have 128 (or some power of 2) receive buffers, hence
    your mbuf usage.

    Mike "Silby" Silbersack
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  • Next message: Garrett Wollman: "Re: mbuf usage for an idle machine"