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    SubjectRe: swapoff() runs forever
    Am 09.04.2012 20:40, schrieb Hugh Dickins:
    > On Mon, 9 Apr 2012, Richard Weinberger wrote:
    >> Am 09.04.2012 07:35, schrieb Konstantin Khlebnikov:
    >>> Richard Weinberger wrote:
    >>>> Hi!
    >>>>
    >>>> I'm observing a strange issue (at least on UML) on recent Linux kernels.
    >>>> If swap is being used the swapoff() system call never terminates.
    >>>> To be precise "while ((i = find_next_to_unuse(si, i)) != 0)" in try_to_unuse()
    >>>> never terminates.
    >>>>
    >>>> The affected machine has 256MiB ram and 256MiB swap.
    >>>> If an application uses more than 256MiB memory swap is being used.
    >>>> But after the application terminates the free command still reports that a few
    >>>> MiB are on my swap device and swappoff never terminates.
    >>>
    >>> After last tmpfs changes swapoff can take minutes.
    >>> Or this time it really never terminates?
    >>
    >> I've never waited forever. ;-)
    >
    > Your lack of dedication is disappointing.
    >
    >> Once I've waited for>30 minutes.
    >>
    >> I don't think that it's related to tmpfs because it happens
    >> also while shutting down the system after all filesystems have been unmounted.
    >
    > Like you I'd assume that it is really was going to be forever,
    > rather than swapoff just being characteristically slow:
    > a few MiB left on swap shouldn't take long to get off.
    >
    > I've not seen any such issue in recent months (or years), but
    > I've not been using UML either. The most likely cause that springs
    > to mind would be corruption of the vmalloc'ed swap map: that would
    > be very likely to cause such a hang.

    Okay, I'll dig into this.

    > You say "recent Linux kernels": I wonder what "recent" means.
    > Is this something you can reproduce quickly and reliably enough
    > to do a bisection upon?
    >

    It happens quite reliably on 3.2 and 3.3.
    On 3.1 and 3.0 sometimes.
    I've already wasted half a day with bisecting it.

    Thanks,
    //richard


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