KSM not working in 4.9 Kernel

Pintu Kumar pintu.ping at gmail.com
Mon Sep 17 04:55:27 PDT 2018


On Mon, Sep 17, 2018 at 11:46 AM Pintu Kumar <pintu.ping at gmail.com> wrote:
> > > But still no effect.
> > > And I checked LTP test cases. It almost doing the same thing.
> > >
> > > I observed that [ksmd] thread is not waking up at all.
> > > I gave some print inside it, but I could never saw that prints coming.
> > > I could not find it running either in top command during the operation.
> > > Is there anything needs to be done, to wakw up ksmd?
> > > I already set: echo 1 > /sys/kernel/mm/ksm.
> >
> > It should be echo 1 > /sys/kernel/mm/ksm/run
> >
>
> Oh yes, sorry for the typo.
> I tried the same, but still ksm is not getting invoked.
> Could someone confirm if KSM was working in 4.9 kernel?
>

Ok, it's working now. I have to explicitly stop the ksm thread to see
the statistics.
Also there was some internal patch that was setting vm_flags to
VM_MERGABLE thus causing ksm_advise call to return.

# echo 1 > /sys/kernel/mm/ksm/run
# ./malloc-test.out &
# echo 0 > /sys/kernel/mm/ksm/run

~ # grep -H '' /sys/kernel/mm/ksm/*
/sys/kernel/mm/ksm/full_scans:105
/sys/kernel/mm/ksm/pages_shared:1
/sys/kernel/mm/ksm/pages_sharing:999
/sys/kernel/mm/ksm/pages_to_scan:100
/sys/kernel/mm/ksm/pages_unshared:0
/sys/kernel/mm/ksm/pages_volatile:0
/sys/kernel/mm/ksm/run:0
/sys/kernel/mm/ksm/sleep_millisecs:20


However, I have one doubt.
Is the above data correct, for the below program?

int main(int argc, char *argv[])
{
        int i, n, size, ret;
        char *buffer;
        void *addr;

        n = 10;
        size = 100 * getpagesize();
        for (i = 0; i < n; i++) {
                buffer = (char *)malloc(size);
                memset(buffer, 0xff, size);
                madvise(buffer, size, MADV_MERGEABLE);
                addr =  mmap(NULL, size,
                           PROT_READ | PROT_EXEC | PROT_WRITE,
MAP_PRIVATE | MAP_ANONYMOUS,
                           -1, 0);
                memset(addr, 0xff, size);
                ret = madvise(addr, size, MADV_MERGEABLE);
                if (ret < 0) {
                        fprintf(stderr, "madvise failed: ret: %d,
reason: %s\n", ret, strerror(errno));
                }
                usleep(500);
        }
        printf("Done....press ^C\n");

        pause();

        return 0;
}


Thanks,
Pintu



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