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    SubjectRe: [regression -next0117] What is kcompactd and why is he eating 100% of my cpu?
    Greetings!

    I don't know if it still actual, but I am strugling with this problem right now and searching the internet for solutions.
    I read the thread and saw that you are strugling to reproduce the problem, and I can reproduce it almost every day.

    - Install vmware player, and a linux guest.
    - Configure the virtual machine to have a good amount of memory and cpu
    - run resource intensive tasks on the guest
    - when the host used up almost it's all memory and start to reuse caches kcompactd will kick in.

    As I know the problem is related to transparent huge pages, but I tried to disable it.
    Today I saw the problem again and kcompactd shown an interesting status in top. It hasn't used any memory, all zeroes but it used up one core completely.

    My machine is a core-i7 with 4 physical cores and hyper threading and 24GB Memory
    5.9.11-arch2-1 #1 SMP PREEMPT Sat, 28 Nov 2020 02:07:22 +0000 x86_64 GNU/Linux

    Hope this can help, to point out the problem.

    Tibor Bana

    On Wed, 30 Jan 2019 10:40:20 +0000
    Mel Gorman <mgorman@techsingularity.net> wrote:

    > On Tue, Jan 29, 2019 at 11:29:37PM -0500, valdis.kletnieks@vt.edu wrote:
    > > On Tue, 29 Jan 2019 20:06:39 -0500, valdis.kletnieks@vt.edu said:
    > > > On Mon, 28 Jan 2019 10:16:27 +0100, Jan Kara said:
    > > >
    > > > > So my buffer_migrate_page_norefs() is certainly buggy in its current
    > > > > incarnation (as a result block device page cache is not migratable at all).
    > > > > I've sent Andrew a patch over week ago but so far it got ignored. The patch
    > > > > is attached, can you give it a try whether it changes something for you?
    > > > > Thanks!
    > > >
    > > > Been running with the patch for about 24 hours, haven't seen kcompactd
    > > > misbehave. I even fired up a Chrome with a lot of tabs open, a Firefox, and a
    > > > kernel build, intentionally drove the system into swapping, and kcompactd
    > > > didn't make it into the top 10 on 'top'.
    > > >
    > > > I'm willing to say put a "tested-by:" on that one, it looks fixed from here.
    > > > If there's any remaining bugs, they're ones I can't seem to trigger...
    > >
    > > Spoke too soon. Sitting here not stressing the laptop at all, plenty of free
    > > memory, and ka-blam.
    > >
    > > Will keep my eyes open and do the data gathering Mel Gorban wanted - I discovered
    > > too late that trace-cmd wasn't installed, and things broke free by themselves (probably
    > > not coincidence that I launched a terminal window and then it cleared....)
    > >
    >
    > That's unfortunate. I also note that linux-next still has not been
    > updated with the latest version of the compaction series. Nevertheless,
    > it might be helpful to get the output of
    >
    > grep -r . /sys/kernel/mm/transparent_hugepage/*
    >
    > and the trace when the system is in normal use but kcompactd has not
    > pegged at 100%. At minimum, I'd like to see what the sources of high-order
    > allocations are and the likely causes of wakeups of kcompactd in case
    > there are any hints there. Your Kconfig is also potentially useful.
    >
    > Thanks.
    >
    > --
    > Mel Gorman
    > SUSE Labs


    --
    Tibor Bana <bana.tibor@gmail.com>

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