Re: Call for testers: New PID allocator patch for -CURRENT

From: Terry Lambert (tlambert2_at_mindspring.com)
Date: 02/03/04

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    Date: Tue, 03 Feb 2004 01:55:41 -0800
To: Peter Jeremy <PeterJeremy@optushome.com.au>

    [ ... dropping -hackers and leaving -current in ... ]

    Peter Jeremy wrote:
    > Note that many system utilities "know" that pids can be represented
    > in 5 digits and having max_pid exceed 99999 will disrupt output from
    > top, ps, lsof, pstat etc. This places an upper limit on how high
    > max_pid can be realistically tuned.

    Personally, I don't think this really matters; probably the correct
    thing to do if this was an issue would be to cut down the column with
    the command name in it. The thing that really matters is the delimiter
    character for "cut -d" for scripts, which should be using that method,
    rather than specific column data. Alternately, for ps, you could set
    the "COLUMNS" environment variable to a large number and/or use the "-www"
    argument.

    FWIW: The hard and fast limit is actually 0x000fffff, from event.h,
    because of the way kevents are handled for EVFILT_PROC to stuff the
    PID into the hints fiels. Practically, this works out to 1048575,
    before you run out of bits to represent the PID.

    Jeffrey Hsu submitted a patch for this once, and I submitted a patch
    for this once, which added a separate hint field internally (and added
    support for System V IPC kevents). A side effect of this patch is to
    permit contracts betwen user space and the kernel event filters, which
    can't be done without the address of a structure, which is one of the
    things I was passing around as the (now larger) hint.

    In other words, it fixes the Linux complaint about "edge vs. level"
    that has kept them from adopting the kqueue/kevent interfaces, by
    letting you have a choice in the events, and/or pass around a larger
    event buffer for multiple events to be copied out, etc..

    -- Terry
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