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    SubjectRe: [PROBLEM] hard-lock with kmemtrace, relayfs, and splice
    On Sat, Oct 25, 2008 at 08:56:07AM +0800, Peter Teoh wrote:
    > ok. just ignore it. i think based on "git log" of
    > "git://repo.or.cz/linux-2.6/kmemtrace.git":
    >
    > commit 0441e5ff6ab71cf7a3e9ec3116f14d0fd7d20d51
    > Author: Eduard - Gabriel Munteanu <eduard.munteanu@linux360.ro>
    > Date: Thu Jul 10 20:20:05 2008 +0300
    >
    > kmemtrace: SLOB hooks.
    >
    > the repo seemed way out of date. But a clone of Pekka's slab-2.6's
    > topic/kmemtrace branch have no problem. The steps are as follows:
    >
    > 1. git clone git://git.kernel.org/pub/scm/linux/kernel/git/penberg/slab-2.6.git
    > 2. git checkout -m origin/topic/kmemtrace
    > 3. git checkout -b kmemtrace

    Hi,

    Yes, that repo may be outdated, please use Pekka's for the latest
    working stuff.

    > git log gives:
    >
    > commit 51b19be3535c8fbcce6b6f838d89b9a6a4cc5b92
    > Author: Tom Zanussi <zanussi@comcast.net>
    > Date: Fri Oct 10 23:58:51 2008 -0500
    >
    > relayfs: fix infinite loop with splice()
    >
    > But the userspace tool I still get it from: git://repo.or.cz/kmemtrace-user.git
    >
    > Correct?

    Yes, I maintain this one and it's up-to-date.

    > Now I have some problems:
    >
    > a. I would like to extract out all the commit as diff - may I know
    > how to do that? ("git log" only gives the descriptive part).

    You can use "git-log -p" to get diffs along with commit history.

    > b. boot-time memory profiling....how can it be done (or extracted
    > out)? (kmemtrace-user does not have that?)

    If you enable kmemtrace at boot-time using the "kmemtrace.enabled=yes"
    parameter, kmemtrace will start logging just after kmem_cache_init()
    finishes. There are plans for making tracing possible even earlier,
    however it involves quite a big rework of how relay allocates its
    buffers.

    > c. please provide some pointers to documentation: how do I
    > interpret the following:
    >
    > Allocation #83468 (CPU0) already exists!
    > by __kmalloc_track_caller+25
    > last touched by __kmalloc_track_caller
    > Allocation #83740 (CPU0) already exists!
    > by __kmalloc_track_caller+25
    > last touched by __kmalloc_track_caller

    The userspace app writes out those messages when it looks like a memory
    region has been allocated twice. In reality, it's most likely a free
    hasn't been traced (because a misc free function isn't traced).

    > For my purpose, I would like to trace how and where is memory
    > allocated - just one one single userspace program which access the
    > mmap("/dev/mem") to read the memory. How can it be done? "Tracing
    > memory" in my context will mean list all the kernel-function +
    > memory-allocated-within-the-function + its-PFN-or-PTE-information (to
    > pinpoint the exact physical page). My understanding is that these
    > can be done, via checking the value of "current", as each userspace
    > program started will have a unique "current" context value, and
    > therefore within any kernel function, just check this value, to focus
    > tracing on just one particular userspace program. Correct?

    I have made provisions for exporting the whole stack trace, however it
    is not yet implemented.

    > d. The following:
    >
    > /sys/kernel/debug/kmemtrace>ls -al
    > ???? 0
    > drwxr-xr-x 2 root root 0 2008-10-25 .
    > drwxr-xr-x 9 root root 0 2008-10-25 ..
    > -r-------- 1 root root 0 2008-10-25 abi_version
    > -r-------- 1 root root 2946936192 2008-10-25 cpu0
    > -r-------- 1 root root 1701263952 2008-10-25 cpu1
    > -rw------- 1 root root 0 2008-10-25 enabled
    > -r-------- 1 root root 0 2008-10-25 total_overruns
    >
    > So the information is stored in memory, right? Is it possible to
    > reset it? I don't want these information to clog up the memory.

    Relay uses fixed size buffers, so there is no point in clearing them.

    > e. The balance between cpu0 and cpu1 does not seemed equal, any
    > implications on the scheduler/ IO Scheduler? or memory allocation
    > scheduler (if there exists one :-))....sorry about that....my
    > knowledge is limited.

    Much of the booting sequence is done on a single CPU, then the kernel
    switches to SMP. It is natural to see one CPU log more allocations.

    > --
    > Regards,
    > Peter Teoh

    Thanks for testing.


    Cheers,
    Eduard



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