Re: KSM not working in 4.9 Kernel

[Pintu Kumar]

On Sun, Sep 16, 2018 at 9:02 PM Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx> wrote:
>
> On Fri, Sep 14, 2018 at 07:58:01PM +0530, Pintu Kumar wrote:
> > Hi All,
> >
> > Board: Hikey620 ARM64
> > Kernel: 4.9.20
> >
> > I am trying to verify KSM (Kernel Same Page Merging) functionality on
> > 4.9 Kernel using "mmap" and madvise user space test utility.
> > But to my observation, it seems KSM is not working for me.
> > CONFIG_KSM=y is enabled in kernel.
> > ksm_init is also called during boot up.
> >   443 ?        SN     0:00 [ksmd]
> >
> > ksmd thread is also running.
> >
> > However, when I see the sysfs, no values are written.
> > ~ # grep -H '' /sys/kernel/mm/ksm/*
> > /sys/kernel/mm/ksm/pages_hashed:0
> > /sys/kernel/mm/ksm/pages_scanned:0
> > /sys/kernel/mm/ksm/pages_shared:0
> > /sys/kernel/mm/ksm/pages_sharing:0
> > /sys/kernel/mm/ksm/pages_to_scan:200
> > /sys/kernel/mm/ksm/pages_unshared:0
> > /sys/kernel/mm/ksm/pages_volatile:0
> > /sys/kernel/mm/ksm/run:1
> > /sys/kernel/mm/ksm/sleep_millisecs:1000
> >
> > So, please let me know if I am doing any thing wrong.
> >
> > This is the test utility:
> > int main(int argc, char *argv[])
> > {
> >         int i, n, size;
> >         char *buffer;
> >         void *addr;
> >
> >         n = 100;
> >         size = 100 * getpagesize();
> >         for (i = 0; i < n; i++) {
> >                 buffer = (char *)malloc(size);
> >                 memset(buffer, 0xff, size);
> >                 addr =  mmap(NULL, size,
> >                            PROT_READ | PROT_EXEC | PROT_WRITE,
> > MAP_PRIVATE | MAP_ANONYMOUS,
> >                            -1, 0);
> >                 madvise(addr, size, MADV_MERGEABLE);
>
> Just mmap'ing an area does not allocate any physical pages, so KSM has
> nothing to merge.
>
> You need to memset(addr,...) after mmap().
>

Yes, I am doing memset also.
memset(addr, 0xff, size);

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.



> >                 sleep(1);
> >         }
> >         printf("Done....press ^C\n");
> >
> >         pause();
> >
> >         return 0;
> > }
> >
> >
> >
> > Thanks,
> > Pintu
> >
>
> --
> Sincerely yours,
> Mike.
>