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    SubjectRe: [PATCH 4/4] mm/madvise: allow KSM hints for remote API
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    On Fri, 10 Jan 2020 13:34:33 -0800 Minchan Kim <minchan@kernel.org> wrote:

    > From: Oleksandr Natalenko <oleksandr@redhat.com>
    >
    > It all began with the fact that KSM works only on memory that is marked
    > by madvise(). And the only way to get around that is to either:
    >
    > * use LD_PRELOAD; or
    > * patch the kernel with something like UKSM or PKSM.
    >
    > (i skip ptrace can of worms here intentionally)
    >
    > To overcome this restriction, lets employ a new remote madvise API. This
    > can be used by some small userspace helper daemon that will do auto-KSM
    > job for us.
    >
    > I think of two major consumers of remote KSM hints:
    >
    > * hosts, that run containers, especially similar ones and especially in
    > a trusted environment, sharing the same runtime like Node.js;
    >
    > * heavy applications, that can be run in multiple instances, not
    > limited to opensource ones like Firefox, but also those that cannot be
    > modified since they are binary-only and, maybe, statically linked.
    >
    > Speaking of statistics, more numbers can be found in the very first
    > submission, that is related to this one [1]. For my current setup with
    > two Firefox instances I get 100 to 200 MiB saved for the second instance
    > depending on the amount of tabs.
    >
    > 1 FF instance with 15 tabs:
    >
    > $ echo "$(cat /sys/kernel/mm/ksm/pages_sharing) * 4 / 1024" | bc
    > 410
    >
    > 2 FF instances, second one has 12 tabs (all the tabs are different):
    >
    > $ echo "$(cat /sys/kernel/mm/ksm/pages_sharing) * 4 / 1024" | bc
    > 592
    >
    > At the very moment I do not have specific numbers for containerised
    > workload, but those should be comparable in case the containers share
    > similar/same runtime.
    >
    > [1] https://lore.kernel.org/patchwork/patch/1012142/
    >
    > Signed-off-by: Oleksandr Natalenko <oleksandr@redhat.com>
    > Signed-off-by: Minchan Kim <minchan@kernel.org>

    Reviewed-by: SeongJae Park <sjpark@amazon.de>

    > ---
    > mm/madvise.c | 2 ++
    > 1 file changed, 2 insertions(+)
    >
    > diff --git a/mm/madvise.c b/mm/madvise.c
    > index eb42b2b7f49b..3aa9aec6bfd9 100644
    > --- a/mm/madvise.c
    > +++ b/mm/madvise.c
    > @@ -1000,6 +1000,8 @@ process_madvise_behavior_valid(int behavior)
    > switch (behavior) {
    > case MADV_COLD:
    > case MADV_PAGEOUT:
    > + case MADV_MERGEABLE:
    > + case MADV_UNMERGEABLE:
    > return true;
    > default:
    > return false;
    > --
    > 2.25.0.rc1.283.g88dfdc4193-goog

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