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    SubjectRe: iotop: khugepaged at 99.99% (
    On Thursday 12 May 2011 16:03:52 Andrea Arcangeli wrote:
    > Hi Ulrich,
    > On Wed, May 11, 2011 at 10:53:18AM +0000, Ulrich Keller wrote:
    > > I am seeing exactly the same symptoms on my Lenovo T60 Core2 duo, 3GB
    > > RAM, running Arch Linux i686 with Kernel When I've heavily
    > > used Firefox for a while, or used R with high memory usage (>1 GB),
    > > individual applications become unresponsive, new processes fail to start
    > > and after a while the whole system freezes. When it happens, iotop shows
    > > khugepaged and sometimes firefox at 99.99%.
    > >
    > > I'd be happy to post information here when the problem occurs again.
    > > Anything other than "cat /proc/zoneinfo"?
    > SYSRQ+T run multiple times during the hang and /proc/zoneinfo as well
    > run multiple times during the hang is the best info we can have for
    > now, /proc/zoneinfo is the most interesting as it will show us the
    > values that the too_many_isolated loop is checking to decide if to
    > continue looping. Even better would be a crash dump, but you may not
    > have the setup for that.
    > The patch I posted likely fixes it, but it may not be the right fix. I
    > don't really like that logic anyway but if that logic is not the
    > problem and the stat accounting is not correct, clearly we can defer
    > changing too_many_isolated and focus on the real problem first.
    > It may not be something new, it may have been exposed by the
    > __GFP_NO_KSWAPD flag, kswapd is always immune from the
    > too_many_isolated loop, so it keeps the VM rolling and would normally
    > hide such problem if it ever happened before. It might also be be
    > something wrong with the THP altered statistics (counting 512 pages
    > for each THP), in that case it would be THP specific, but I wonder why
    > it's not easy to reproduce.
    > So you've 2 cores, and probably a SMP kernel right? Is it a preempt
    > kernel (just in case it makes any difference.. I doubt)? i386 means
    > it's a 32bit kernel? Or you meant i386 to say x86? The previous report
    > is also on a 32bit kernel. 32bit didn't get nearly the same amount of
    > testing of 64bit, but it's hard to see how 32bit could matter here!
    > Could you both send your .config (the UP one from Thomas, and the one
    > from your core2duo laptop).
    > CONFIG_TASK_XACCT, TASK_IO_ACCOUNTING all =y right? Not everyone is
    > running iotop you both are (before this bugreport I had TASKSTAT=n and
    > I still have on most systems), so maybe it's something related to
    > TASKSTATS corrupting memory or screwing the accounting when iotop
    > runs? That's just an idea not to exclude even if almost certainly not
    > realistic. Did it ever happen on a system with TASKSTAT=n or not
    > running iotop to rule it out? (likely even if it's buggy, it won't be
    > noticeable unless iotop runs)
    > Being reproduced on UP probably means the per-cpu vmstat.c is not to
    > blame (especially if it happens both UP and SMP builds, and if preempt
    > is confirmed disabled).
    > We've to restrict the scope of the bug a bit and try to find commons in
    > the .config too.
    > Here I've no sign of hang from too_many_isolated from 39rc6 and I'm
    > sure it never occurred to me in the past.
    > Thanks a lot,
    > Andrea

    Is there any progress on this? I've observed this behavior different times too,
    with kernel 2.6.39-rc7. After a while working some processes (kmail,
    akregator, konqueror) got stuck in D state together with the khugepaged task.
    I could kill the hanging process (kill -n 9) but the khugepaged task stayed in
    D state.
    The system is a Pentium M (Banias) with 1.3GHz and 1.5G RAM. Attached is the
    output from multiple SYSRQ+T, content from /proc/zoneinfo and the config.

    [unhandled content-type:application/x-bzip-compressed-tar]
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