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    SubjectRe: init's children list is long and slows reaping children.
    On Mon, 09 Apr 2007 18:48:54 -0600
    ebiederm@xmission.com (Eric W. Biederman) wrote:

    > Andrew Morton <akpm@linux-foundation.org> writes:
    >
    > > I suspect there are quite a few kernel threads which don't really need to
    > > be threads at all: the code would quite happily work if it was changed to
    > > use keventd, via schedule_work() and friends. But kernel threads are
    > > somewhat easier to code for.
    > >
    > > I also suspect that there are a number of workqueue threads which
    > > could/should have used create_singlethread_workqueue(). Often this is
    > > because the developer just didn't think to do it.
    > >
    > > otoh, a lot of these inefficeincies are probably down in scruffy drivers
    > > rather than in core or top-level code.
    > >
    > > <I also wonder where all these parented-by-init,
    > > presumably-not-using-kthread kernel threads are coming from>
    >
    >
    > >From another piece of this thread.

    Yeah, sorry. Without mentioning any names, someone@tv-sign.ru broke the
    threading so I came in halfway.

    > > > Robin how many kernel thread per cpu are you seeing?
    > >
    > > 10.
    > >
    > > FYI, pid 1539 is kthread.
    > >
    > > a01:~ # ps -ef | egrep "\[.*\/255\]"
    > > root 512 1 0 Apr08 ? 00:00:00 [migration/255]
    > > root 513 1 0 Apr08 ? 00:00:00 [ksoftirqd/255]
    > > root 1281 1 0 Apr08 ? 00:00:02 [events/255]
    > > root 2435 1539 0 Apr08 ? 00:00:00 [kblockd/255]
    > > root 3159 1539 0 Apr08 ? 00:00:00 [aio/255]
    > > root 4007 1539 0 Apr08 ? 00:00:00 [cqueue/255]
    > > root 8653 1539 0 Apr08 ? 00:00:00 [ata/255]
    > > root 17438 1539 0 Apr08 ? 00:00:00 [xfslogd/255]
    > > root 17950 1539 0 Apr08 ? 00:00:00 [xfsdatad/255]
    > > root 18426 1539 0 Apr08 ? 00:00:00 [rpciod/255]
    >
    >
    > So it looks like there were about 1500 kernel threads that started up before
    > kthread started.
    >
    > So the kernel threads appear to have init as their parent is because
    > they started before kthread for the most part.
    >
    > At 10 kernel threads per cpu there may be a little bloat but it isn't
    > out of control. It is mostly that we are observing the kernel as
    > NR_CPUS approaches infinity. 4096 isn't infinity yet but it's easily
    > a 1000 fold bigger then most people are used to :)

    Yes, I expect we could run init_workqueues() much earlier, from process 0
    rather than from process 1. Something _might_ blow up as it often does when
    we change startup ordering, but in this case it would be somewhat surprising.

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