Messages in this thread Patch in this message | | | From | Minchan Kim <> | Subject | [PATCH 4/4] mm/madvise: allow KSM hints for remote API | Date | Fri, 10 Jan 2020 13:34:33 -0800 |
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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> --- 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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