KSM not working in 4.9 Kernel

Mike Rapoport rppt at linux.vnet.ibm.com
Sun Sep 16 21:37:24 PDT 2018


On Sun, Sep 16, 2018 at 10:35:17PM +0530, Pintu Kumar wrote:
> On Sun, Sep 16, 2018 at 9:02 PM Mike Rapoport <rppt at linux.vnet.ibm.com> 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.

It should be echo 1 > /sys/kernel/mm/ksm/run
 
> 
> 
> > >                 sleep(1);
> > >         }
> > >         printf("Done....press ^C\n");
> > >
> > >         pause();
> > >
> > >         return 0;
> > > }
> > >
> > >
> > >
> > > Thanks,
> > > Pintu
> > >
> >
> > --
> > Sincerely yours,
> > Mike.
> >
> 

-- 
Sincerely yours,
Mike.




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