Re: [PATCH 4/4] mm/madvise: allow KSM hints for remote API
From: SeongJae Park <hidden>
Date: 2020-01-11 07:43:09
Also in:
linux-mm, lkml
On Fri, 10 Jan 2020 13:34:33 -0800 Minchan Kim [off-list ref] wrote:
From: Oleksandr Natalenko <redacted>
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 <redacted>
Signed-off-by: Minchan Kim <minchan@kernel.org>Reviewed-by: SeongJae Park <redacted>
quoted hunk
--- 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