On Fri, Mar 06, 2020 at 05:08:18PM +0100, Vlastimil Babka wrote: > On 3/6/20 2:41 PM, Oleksandr Natalenko wrote: > > 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; > > Ah, I forgot to ask, given the discussion of races in patch 2 (Question 2), > where android can stop the tasks to apply the madvise hints in a race-free > manner, how does that work for remote KSM hints in your scenarios, especially > the one above? We have cgroup.freeze for that. > > >> > > >> > * 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? > > Dunno, it's nice to react to signals quickly, for any proces that gets them, no? So, do you mean something like this? === diff --git a/mm/ksm.c b/mm/ksm.c index 363ec8189561..b39c237cfcf4 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -849,7 +849,8 @@ static int unmerge_ksm_pages(struct vm_area_struct *vma, for (addr = start; addr < end && !err; addr += PAGE_SIZE) { if (ksm_test_exit(vma->vm_mm)) break; - if (signal_pending(current)) + if (signal_pending(current) || + signal_pending(rcu_dereference(vma->vm_mm->owner))) err = -ERESTARTSYS; else err = break_ksm(vma, addr); === BTW, this won't work with !CONFIG_MEMCG, so probably task_struct should be passed through instead. IIUC, this would also require amending struct mm_slot in order to share the same code path with ksmd. I'm not sure I've seen such a culprit anywhere else, so I'm in doubt this would be a correct thing to do. Ideas? > > >> 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
