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    SubjectRe: 2.6.39-rc4+: Kernel leaking memory during FS scanning, regression?
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    On Mon, Apr 25, 2011 at 7:29 PM, Paul E. McKenney
    <paulmck@linux.vnet.ibm.com> wrote:
    > On Mon, Apr 25, 2011 at 07:00:32PM +0200, Bruno Prémont wrote:
    >> On Mon, 25 April 2011 Linus Torvalds wrote:
    >> > 2011/4/25 Bruno Prémont <bonbons@linux-vserver.org>:
    >> > >
    >> > > kmemleak reports 86681 new leaks between shortly after boot and -2 state.
    >> > > (and 2348 additional ones between -2 and -4).
    >> >
    >> > I wouldn't necessarily trust kmemleak with the whole RCU-freeing
    >> > thing. In your slubinfo reports, the kmemleak data itself also tends
    >> > to overwhelm everything else - none of it looks unreasonable per se.
    >> >
    >> > That said, you clearly have a *lot* of filp entries. I wouldn't
    >> > consider it unreasonable, though, because depending on load those may
    >> > well be fine. Perhaps you really do have some application(s) that hold
    >> > thousands of files open. The default file limit is 1024 (I think), but
    >> > you can raise it, and some programs do end up opening tens of
    >> > thousands of files for filesystem scanning purposes.
    >> >
    >> > That said, I would suggest simply trying a saner kernel configuration,
    >> > and seeing if that makes a difference:
    >> >
    >> > > Yes, it's uni-processor system, so SMP=n.
    >> > > TINY_RCU=y, PREEMPT_VOLUNTARY=y (whole /proc/config.gz attached keeping
    >> > > compression)
    >> >
    >> > I'm not at all certain that TINY_RCU is appropriate for
    >> > general-purpose loads. I'd call it more of a "embedded low-performance
    >> > option".
    >>
    >> Well, TINY_RCU is the only option when doing PREEMPT_VOLUNTARY on
    >> SMP=n...
    >
    > You can either set SMP=y and NR_CPUS=1 or you can handed-edit
    > init/Kconfig to remove the dependency on SMP.  Just change the
    >
    >        depends on !PREEMPT && SMP
    >
    > to:
    >
    >        depends on !PREEMPT
    >
    > This will work fine, especially for experimental purposes.
    >
    >> > The _real_ RCU implementation ("tree rcu") forces quiescent states
    >> > every few jiffies and has logic to handle "I've got tons of RCU
    >> > events, I really need to start handling them now". All of which I
    >> > think tiny-rcu lacks.
    >>
    >> Going to try it out (will take some time to compile), kmemleak disabled.
    >>
    >> > So right now I suspect that you have a situation where you just have a
    >> > simple load that just ends up never triggering any RCU cleanup, and
    >> > the tiny-rcu thing just keeps on gathering events and delays freeing
    >> > stuff almost arbitrarily long.
    >>
    >> I hope tiny-rcu is not that broken... as it would mean driving any
    >> PREEMPT_NONE or PREEMPT_VOLUNTARY system out of memory when compiling
    >> packages (and probably also just unpacking larger tarballs or running
    >> things like du).
    >
    > If it is broken, I will fix it.  ;-)
    >
    >                                                        Thanx, Paul
    >
    >> And with system doing nothing (except monitoring itself) memory usage
    >> goes increasing all the time until it starves (well it seems to keep
    >> ~20M free, pushing processes it can to swap). Config is just being
    >> make oldconfig from working 2.6.38 kernel (answering default for new
    >> options)
    >>
    >> Memory usage evolution graph in first message of this thread:
    >> http://thread.gmane.org/gmane.linux.kernel.mm/61909/focus=1130480
    >>
    >> Attached graph matching numbers of previous mail. (dropping caches was at
    >> 17:55, system idle since then)
    >>
    >> Bruno
    >>
    >>
    >> > So try CONFIG_PREEMPT and CONFIG_TREE_PREEMPT_RCU to see if the
    >> > behavior goes away. That would confirm the "it's just tinyrcu being
    >> > too dang stupid" hypothesis.
    >> >
    >> >                      Linus
    >
    >
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    >

    Hi,

    I was playing with Debian's kernel-buildsystem for -rc4 with a
    self-defined '686-up' so-called flavour.

    Here I have a Banias Pentium-M (UP, *no* PAE) and still experimenting
    with kernel-config options.

    CONFIG_X86_UP_APIC=y
    CONFIG_X86_UP_IOAPIC=y

    ...is not possible with CONFIG_SMP=y

    These settings are possible by not hacking existing Kconfigs:

    $ egrep 'M486|M686|X86_UP|CONFIG_SMP|NR_CPUS|PREEMPT|_RCU|_HIGHMEM|PAE'
    debian/build/build_i386_none_686-up/.config
    CONFIG_TREE_PREEMPT_RCU=y
    # CONFIG_TINY_RCU is not set
    # CONFIG_TINY_PREEMPT_RCU is not set
    CONFIG_PREEMPT_RCU=y
    # CONFIG_RCU_TRACE is not set
    CONFIG_RCU_FANOUT=32
    # CONFIG_RCU_FANOUT_EXACT is not set
    # CONFIG_TREE_RCU_TRACE is not set
    CONFIG_PREEMPT_NOTIFIERS=y
    # CONFIG_SMP is not set
    # CONFIG_M486 is not set
    CONFIG_M686=y
    CONFIG_NR_CPUS=1
    # CONFIG_PREEMPT_NONE is not set
    # CONFIG_PREEMPT_VOLUNTARY is not set
    CONFIG_PREEMPT=y
    CONFIG_X86_UP_APIC=y
    CONFIG_X86_UP_IOAPIC=y
    CONFIG_HIGHMEM4G=y
    # CONFIG_HIGHMEM64G is not set
    CONFIG_HIGHMEM=y
    CONFIG_DEBUG_PREEMPT=y
    # CONFIG_SPARSE_RCU_POINTER is not set
    # CONFIG_DEBUG_HIGHMEM is not set
    # CONFIG_RCU_TORTURE_TEST is not set
    # CONFIG_RCU_CPU_STALL_DETECTOR is not set
    # CONFIG_PREEMPT_TRACER is not set

    But I also see these warnings:

    .config:2106:warning: override: TREE_PREEMPT_RCU changes choice state
    .config:2182:warning: override: PREEMPT changes choice state

    Not sure how to interprete them, so I am a bit careful :-).

    ( Untested - not compiled yet! )

    - Sedat -
    --
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