Re: [PATCH 4/4] mm/madvise: allow KSM hints for remote API

SeongJae Park
2020-01-11T07:43:10Z

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