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Message-Id: <20180921081626.GA12492@rapoport-lnx>
Date: Fri, 21 Sep 2018 11:16:27 +0300
From: Mike Rapoport <rppt@...ux.vnet.ibm.com>
To: Pintu Kumar <pintu.ping@...il.com>
Cc: 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: Re: KSM not working in 4.9 Kernel
On Thu, Sep 20, 2018 at 05:21:20PM +0530, Pintu Kumar wrote:
> Hi,
>
> Thank you so much for all your reply so far.
> I have few more doubts to understand the output from ksm sysfs.
> Device: Hikey620 - ARM64 - Linux 4.9.20
> With HUGE page enabled:
> CONFIG_TRANSPARENT_HUGEPAGE=y
> CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS=y
> # CONFIG_TRANSPARENT_HUGEPAGE_MADVISE is not set
>
> Currently, I get this output, when I run below program with ksm:
>
> ~ # grep -H '' /sys/kernel/mm/ksm/*
> /sys/kernel/mm/ksm/full_scans:29
> /sys/kernel/mm/ksm/page_comparisons:39584
> /sys/kernel/mm/ksm/pages_hashed:11672
> /sys/kernel/mm/ksm/pages_scanned:21766
> /sys/kernel/mm/ksm/pages_shared:3
> /sys/kernel/mm/ksm/pages_sharing:10097
> /sys/kernel/mm/ksm/pages_to_scan:200
> /sys/kernel/mm/ksm/pages_unshared:53
> /sys/kernel/mm/ksm/pages_volatile:1
> /sys/kernel/mm/ksm/run:0
> /sys/kernel/mm/ksm/sleep_millisecs:1000
> ---------------------------
>
> int main(int argc, char *argv[])
> {
> int i, n, size, ret;
> char *buffer;
> void *addr;
>
> n = 100;
> size = 100 * getpagesize();
> for (i = 0; i < n; i++) {
> buffer = (char *)malloc(size);
> memset(buffer, 0xff, size);
> madvise(buffer, size, MADV_MERGEABLE);
> if (ret < 0) {
> fprintf(stderr, "malloc madvise failed: ret:
> %d, reason: %s\n", ret, strerror(errno));
> }
> usleep(500);
> }
> printf("Done....press ^C\n");
> pause();
> return 0;
> }
> Note: madvise() system call is not failing here, as mentioned earlier.
> I guess the page is aligned with getpagesize().
> Then I do this to invoke ksm:
> # echo 1 > /sys/kernel/mm/ksm/run
> # ./malloc-test.out &
> # sleep 5
> # echo 0 > /sys/kernel/mm/ksm/run
> #
>
> Also, the anon pages in the system shows like this:
> BEFORE:
> -------------
> ~ # cat /proc/meminfo | grep -i anon
> Active(anon): 40740 kB
> Inactive(anon): 0 kB
> AnonPages: 40760 kB
> AnonHugePages: 0 kB
>
> AFTER MERGING:
> --------------------------
> ~ # cat /proc/meminfo | grep -i anon
> Active(anon): 440 kB
> Inactive(anon): 0 kB
> AnonPages: 188 kB
> AnonHugePages: 0 kB
>
> I want to understand the KSM output w.r.t to the above program, and
> cross-check if the output is correct.
> Can someone help me to understand it?
>
> As of now, what I understood is that:
> - I am allocating around 400KB of memory 100 times. That is: 100 * 100
> * 4K = 10000 pages (which are all with similar content).
> - Output says: 10097 page_sharing happened.
> - Pages currently shared is: 3
> - So total pages are: 10097 + 3 = 10100
>
> I could not understand from where the additional 100 pages came from?
> Also, why some pages are shown as: pages_unshared ?
> What can I interpret from this?
> And, what does it mean by: pages_volatile:1 ?
>
> Basically, I wanted to understand, is there any problem with the above
> output, or it is fine.
> If it is fine, how to prove it?
The ksm sysfs attributes are described at
Documentation/admin-guide/mm/ksm.rst or online at [1].
The numbers look sane in general. The additional pages may come from malloc
metadata that is created by libc when you allocate memory.
I'd recommend to use mmap() or posix_memalign() with page size alignment to
get exact amount of page aligned memory.
[1] https://www.kernel.org/doc/html/latest/admin-guide/mm/ksm.html
> Thanks,
> Pintu
>
> On Mon, Sep 17, 2018 at 8:29 PM Mike Rapoport <rppt@...ux.vnet.ibm.com> wrote:
> >
> > On Mon, Sep 17, 2018 at 05:25:27PM +0530, Pintu Kumar wrote:
> > > On Mon, Sep 17, 2018 at 11:46 AM Pintu Kumar <pintu.ping@...il.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?
> >
> > You have 1 shared page and 999 additional references to that page
> >
> > > 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);o
> >
> > This madvise() call should fail because buffer won't be page aligned
> >
> > > 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
> > >
> >
> > --
> > Sincerely yours,
> > Mike.
> >
>
--
Sincerely yours,
Mike.
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