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    SubjectRe: [RFC][PATCH] ps command race fix take2 [1/4] list token
    KAMEZAWA Hiroyuki <> writes:

    > This is ps command race fix take2. Unfortunately, against 2.6.18-rc4.
    > I'll rebase this to appropriate kernel if O.K. (I think this is RFC)
    > This patch implements Paul Jackson's idea, 'inserting false link in task list'.

    Currently the tasklist_lock is one of the more highly contended locks in
    the kernel. Adding an extra place it is taken is undesirable.
    If could see a better algorithm for sending a signal to all processes
    in a process groups we could remove the tasklist_lock entirely.

    In addition you only solves half the readdir problems. You don't solve
    the seek problem which is returning to an offset you had been to
    before. A relatively rare case but...

    > Good point of this approach is cost of searching task is O(N) (N=num of tgids).
    > Bad point is lock and kmalloc/kfree.
    > I didin't modified thread_list and cpuset's proc list, maybe future work.
    > If searching pid bitmap is better, please take Erics.

    My patch at least needs a good changelog but I believe it will work
    better and can be further improved with a better pid data structure
    if there is actually a problem there. Given that I don't take
    any locks it should be much friendlier at scale, and the code
    was simpler.

    However I will miss a few newly forked processes and I don't think your
    technique will miss any. Still neither will miss a process that
    existed the entire time.

    If nothing else I think it was worth posting so we could contrast the two.

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      Last update: 2006-08-22 18:59    [W:0.021 / U:5.940 seconds]
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