From: Oleksandr Natalenko <oleksandr@redhat.com>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Minchan Kim <minchan@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>,
linux-api@vger.kernel.org, Suren Baghdasaryan <surenb@google.com>,
Tim Murray <timmurray@google.com>,
Daniel Colascione <dancol@google.com>,
Sandeep Patil <sspatil@google.com>,
Sonny Rao <sonnyrao@google.com>,
Brian Geffon <bgeffon@google.com>, Michal Hocko <mhocko@suse.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Shakeel Butt <shakeelb@google.com>,
John Dias <joaodias@google.com>,
Joel Fernandes <joel@joelfernandes.org>,
Jann Horn <jannh@google.com>,
alexander.h.duyck@linux.intel.com, sj38.park@gmail.com,
SeongJae Park <sjpark@amazon.de>
Subject: Re: [PATCH v7 7/7] mm/madvise: allow KSM hints for remote API
Date: Mon, 9 Mar 2020 14:11:17 +0100 [thread overview]
Message-ID: <20200309131117.anvyjszaigpoz2kp@butterfly.localdomain> (raw)
In-Reply-To: <a63768c1-3959-563b-376b-1d8d90d79b41@suse.cz>
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@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;
>
> 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@amazon.de>
> >> > Signed-off-by: Oleksandr Natalenko <oleksandr@redhat.com>
> >> > Signed-off-by: Minchan Kim <minchan@kernel.org>
> >>
> >> 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
next prev parent reply other threads:[~2020-03-09 13:11 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-02 19:36 [PATCH v7 0/7] introduce memory hinting API for external process Minchan Kim
2020-03-02 19:36 ` [PATCH v7 1/7] mm: pass task and mm to do_madvise Minchan Kim
2020-03-05 15:48 ` Vlastimil Babka
2020-05-08 18:21 ` Minchan Kim
2020-03-02 19:36 ` [PATCH v7 2/7] mm: introduce external memory hinting API Minchan Kim
2020-03-03 10:33 ` kbuild test robot
2020-03-03 14:57 ` Minchan Kim
2020-03-05 18:15 ` Vlastimil Babka
2020-03-10 22:20 ` Minchan Kim
2020-03-11 0:36 ` Minchan Kim
2020-03-12 12:40 ` Vlastimil Babka
2020-03-12 20:23 ` Minchan Kim
2020-05-08 18:33 ` Minchan Kim
2020-03-02 19:36 ` [PATCH v7 3/7] mm: check fatal signal pending of target process Minchan Kim
2020-03-06 10:22 ` Vlastimil Babka
2020-03-10 22:24 ` Minchan Kim
2020-03-02 19:36 ` [PATCH v7 4/7] pid: move pidfd_get_pid function to pid.c Minchan Kim
2020-03-06 10:57 ` Vlastimil Babka
2020-03-06 11:14 ` Christian Brauner
2020-03-02 19:36 ` [PATCH v7 5/7] mm: support both pid and pidfd for process_madvise Minchan Kim
2020-03-06 11:14 ` Vlastimil Babka
2020-03-11 0:42 ` Minchan Kim
2020-05-08 18:36 ` Minchan Kim
2020-05-08 23:04 ` Andrew Morton
2020-05-09 12:48 ` Christian Brauner
2020-05-09 23:14 ` Minchan Kim
2020-05-12 19:55 ` Suren Baghdasaryan
2020-03-02 19:36 ` [PATCH v7 6/7] mm/madvise: employ mmget_still_valid for write lock Minchan Kim
2020-03-06 12:52 ` Vlastimil Babka
2020-03-06 13:03 ` Oleksandr Natalenko
2020-03-06 16:03 ` Vlastimil Babka
2020-03-09 12:30 ` Oleksandr Natalenko
2020-03-10 22:28 ` Minchan Kim
2020-03-02 19:36 ` [PATCH v7 7/7] mm/madvise: allow KSM hints for remote API Minchan Kim
2020-03-06 13:13 ` Vlastimil Babka
2020-03-06 13:41 ` Oleksandr Natalenko
2020-03-06 16:08 ` Vlastimil Babka
2020-03-09 13:11 ` Oleksandr Natalenko [this message]
2020-03-09 15:08 ` Michal Hocko
2020-03-09 15:19 ` Oleksandr Natalenko
2020-03-09 15:42 ` Vlastimil Babka
2020-03-09 16:03 ` Michal Hocko
2020-06-11 2:21 ` Jann Horn
2020-03-02 21:16 ` [PATCH v7 0/7] introduce memory hinting API for external process Andrew Morton
2020-03-02 21:42 ` Minchan Kim
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