On Fri, Mar 06, 2020 at 02:13:49PM +0100, Vlastimil Babka wrote: > On 3/2/20 8:36 PM, Minchan Kim wrote: > > From: Oleksandr Natalenko <oleksandr@xxxxxxxxxx> > > > > 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/ > > > > Reviewed-by: SeongJae Park <sjpark@xxxxxxxxx> > > Signed-off-by: Oleksandr Natalenko <oleksandr@xxxxxxxxxx> > > Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> > > This will lead to one process calling unmerge_ksm_pages() of another. There's a > (signal_pending(current)) test there, should it check also the other task, > analogically to task 3? Do we care about current there then? Shall we just pass mm into unmerge_ksm_pages and check the signals of the target task only, be it current or something else? > Then break_ksm() is fine as it is, as ksmd also calls it, right? I think break_ksm() cares only about mmap_sem protection, so we should be fine here. > > > --- > > mm/madvise.c | 4 ++++ > > 1 file changed, 4 insertions(+) > > > > diff --git a/mm/madvise.c b/mm/madvise.c > > index e77c6c1fad34..f4fa962ee74d 100644 > > --- a/mm/madvise.c > > +++ b/mm/madvise.c > > @@ -1005,6 +1005,10 @@ process_madvise_behavior_valid(int behavior) > > switch (behavior) { > > case MADV_COLD: > > case MADV_PAGEOUT: > > +#ifdef CONFIG_KSM > > + case MADV_MERGEABLE: > > + case MADV_UNMERGEABLE: > > +#endif > > return true; > > default: > > return false; > > > -- Best regards, Oleksandr Natalenko (post-factum) Principal Software Maintenance Engineer
