linux-kernel - KSM not working in 4.9 Kernel

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Message-ID: <CAOuPNLj1wx4sznrtLdKjcvuTf0dECPWzPaR946FoYRXB6YAGCw@mail.gmail.com>
Date:   Fri, 14 Sep 2018 19:58:01 +0530
From:   Pintu Kumar <pintu.ping@...il.com>
To:     open list <linux-kernel@...r.kernel.org>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org
Subject: KSM not working in 4.9 Kernel

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);
                sleep(1);
        }
        printf("Done....press ^C\n");

        pause();

        return 0;
}

Thanks,
Pintu