From: Michal Hocko <mhocko@kernel.org>
To: Minchan Kim <minchan@kernel.org>
Cc: Daniel Colascione <dancol@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Tim Murray <timmurray@google.com>,
Joel Fernandes <joel@joelfernandes.org>,
Suren Baghdasaryan <surenb@google.com>,
Shakeel Butt <shakeelb@google.com>,
Sonny Rao <sonnyrao@google.com>,
Brian Geffon <bgeffon@google.com>,
Linux API <linux-api@vger.kernel.org>
Subject: Re: [RFC 6/7] mm: extend process_madvise syscall to support vector arrary
Date: Thu, 30 May 2019 08:57:55 +0200 [thread overview]
Message-ID: <20190530065755.GD6703@dhcp22.suse.cz> (raw)
In-Reply-To: <20190530021748.GE229459@google.com>
On Thu 30-05-19 11:17:48, Minchan Kim wrote:
> On Wed, May 29, 2019 at 12:33:52PM +0200, Michal Hocko wrote:
> > On Wed 29-05-19 03:08:32, Daniel Colascione wrote:
> > > On Mon, May 27, 2019 at 12:49 AM Minchan Kim <minchan@kernel.org> wrote:
> > > >
> > > > On Tue, May 21, 2019 at 12:37:26PM +0200, Michal Hocko wrote:
> > > > > On Tue 21-05-19 19:26:13, Minchan Kim wrote:
> > > > > > On Tue, May 21, 2019 at 08:24:21AM +0200, Michal Hocko wrote:
> > > > > > > On Tue 21-05-19 11:48:20, Minchan Kim wrote:
> > > > > > > > On Mon, May 20, 2019 at 11:22:58AM +0200, Michal Hocko wrote:
> > > > > > > > > [Cc linux-api]
> > > > > > > > >
> > > > > > > > > On Mon 20-05-19 12:52:53, Minchan Kim wrote:
> > > > > > > > > > Currently, process_madvise syscall works for only one address range
> > > > > > > > > > so user should call the syscall several times to give hints to
> > > > > > > > > > multiple address range.
> > > > > > > > >
> > > > > > > > > Is that a problem? How big of a problem? Any numbers?
> > > > > > > >
> > > > > > > > We easily have 2000+ vma so it's not trivial overhead. I will come up
> > > > > > > > with number in the description at respin.
> > > > > > >
> > > > > > > Does this really have to be a fast operation? I would expect the monitor
> > > > > > > is by no means a fast path. The system call overhead is not what it used
> > > > > > > to be, sigh, but still for something that is not a hot path it should be
> > > > > > > tolerable, especially when the whole operation is quite expensive on its
> > > > > > > own (wrt. the syscall entry/exit).
> > > > > >
> > > > > > What's different with process_vm_[readv|writev] and vmsplice?
> > > > > > If the range needed to be covered is a lot, vector operation makes senese
> > > > > > to me.
> > > > >
> > > > > I am not saying that the vector API is wrong. All I am trying to say is
> > > > > that the benefit is not really clear so far. If you want to push it
> > > > > through then you should better get some supporting data.
> > > >
> > > > I measured 1000 madvise syscall vs. a vector range syscall with 1000
> > > > ranges on ARM64 mordern device. Even though I saw 15% improvement but
> > > > absoluate gain is just 1ms so I don't think it's worth to support.
> > > > I will drop vector support at next revision.
> > >
> > > Please do keep the vector support. Absolute timing is misleading,
> > > since in a tight loop, you're not going to contend on mmap_sem. We've
> > > seen tons of improvements in things like camera start come from
> > > coalescing mprotect calls, with the gains coming from taking and
> > > releasing various locks a lot less often and bouncing around less on
> > > the contended lock paths. Raw throughput doesn't tell the whole story,
> > > especially on mobile.
> >
> > This will always be a double edge sword. Taking a lock for longer can
> > improve a throughput of a single call but it would make a latency for
> > anybody contending on the lock much worse.
> >
> > Besides that, please do not overcomplicate the thing from the early
> > beginning please. Let's start with a simple and well defined remote
> > madvise alternative first and build a vector API on top with some
> > numbers based on _real_ workloads.
>
> First time, I didn't think about atomicity about address range race
> because MADV_COLD/PAGEOUT is not critical for the race.
> However you raised the atomicity issue because people would extend
> hints to destructive ones easily. I agree with that and that's why
> we discussed how to guarantee the race and Daniel comes up with good idea.
Just for the clarification, I didn't really mean atomicity but rather a
_consistency_ (essentially time to check to time to use consistency).
> - vma configuration seq number via process_getinfo(2).
>
> We discussed the race issue without _read_ workloads/requests because
> it's common sense that people might extend the syscall later.
>
> Here is same. For current workload, we don't need to support vector
> for perfomance point of view based on my experiment. However, it's
> rather limited experiment. Some configuration might have 10000+ vmas
> or really slow CPU.
>
> Furthermore, I want to have vector support due to atomicity issue
> if it's really the one we should consider.
> With vector support of the API and vma configuration sequence number
> from Daniel, we could support address ranges operations's atomicity.
I am not sure what do you mean here. Perform all ranges atomicaly wrt.
other address space modifications? If yes I am not sure we want that
semantic because it can cause really long stalls for other operations
but that is a discussion on its own and I would rather focus on a simple
interface first.
> However, since we don't introduce vector at this moment, we need to
> introduce *another syscall* later to be able to handle multile ranges
> all at once atomically if it's okay.
Agreed.
> Other thought:
> Maybe we could extend address range batch syscall covers other MM
> syscall like mmap/munmap/madvise/mprotect and so on because there
> are multiple users that would benefit from this general batching
> mechanism.
Again a discussion on its own ;)
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2019-05-30 6:57 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20190520035254.57579-1-minchan@kernel.org>
[not found] ` <20190520035254.57579-2-minchan@kernel.org>
2019-05-20 8:16 ` [RFC 1/7] mm: introduce MADV_COOL Michal Hocko
2019-05-20 8:19 ` Michal Hocko
2019-05-20 15:08 ` Suren Baghdasaryan
2019-05-20 22:55 ` Minchan Kim
2019-05-20 22:54 ` Minchan Kim
2019-05-21 6:04 ` Michal Hocko
2019-05-21 9:11 ` Minchan Kim
2019-05-21 10:05 ` Michal Hocko
[not found] ` <20190520035254.57579-4-minchan@kernel.org>
2019-05-20 8:27 ` [RFC 3/7] mm: introduce MADV_COLD Michal Hocko
2019-05-20 23:00 ` Minchan Kim
2019-05-21 6:08 ` Michal Hocko
2019-05-21 9:13 ` Minchan Kim
[not found] ` <20190520035254.57579-6-minchan@kernel.org>
2019-05-20 9:18 ` [RFC 5/7] mm: introduce external memory hinting API Michal Hocko
2019-05-21 2:41 ` Minchan Kim
2019-05-21 6:17 ` Michal Hocko
2019-05-21 10:32 ` Minchan Kim
[not found] ` <20190520035254.57579-7-minchan@kernel.org>
2019-05-20 9:22 ` [RFC 6/7] mm: extend process_madvise syscall to support vector arrary Michal Hocko
2019-05-21 2:48 ` Minchan Kim
2019-05-21 6:24 ` Michal Hocko
2019-05-21 10:26 ` Minchan Kim
2019-05-21 10:37 ` Michal Hocko
2019-05-27 7:49 ` Minchan Kim
2019-05-29 10:08 ` Daniel Colascione
2019-05-29 10:33 ` Michal Hocko
2019-05-30 2:17 ` Minchan Kim
2019-05-30 6:57 ` Michal Hocko [this message]
2019-05-30 8:02 ` Minchan Kim
2019-05-30 16:19 ` Daniel Colascione
2019-05-30 18:47 ` Michal Hocko
[not found] ` <20190520035254.57579-8-minchan@kernel.org>
2019-05-20 9:28 ` [RFC 7/7] mm: madvise support MADV_ANONYMOUS_FILTER and MADV_FILE_FILTER Michal Hocko
2019-05-21 2:55 ` Minchan Kim
2019-05-21 6:26 ` Michal Hocko
2019-05-27 7:58 ` Minchan Kim
2019-05-27 12:44 ` Michal Hocko
2019-05-28 3:26 ` Minchan Kim
2019-05-28 6:29 ` Michal Hocko
2019-05-28 8:13 ` Minchan Kim
2019-05-28 8:31 ` Daniel Colascione
2019-05-28 8:49 ` Minchan Kim
2019-05-28 9:08 ` Michal Hocko
2019-05-28 9:39 ` Daniel Colascione
2019-05-28 10:33 ` Michal Hocko
2019-05-28 11:21 ` Daniel Colascione
2019-05-28 11:49 ` Michal Hocko
2019-05-28 12:11 ` Daniel Colascione
2019-05-28 12:32 ` Michal Hocko
2019-05-28 10:32 ` Minchan Kim
2019-05-28 10:41 ` Michal Hocko
2019-05-28 11:12 ` Minchan Kim
2019-05-28 11:28 ` Michal Hocko
2019-05-28 11:42 ` Daniel Colascione
2019-05-28 11:56 ` Michal Hocko
2019-05-28 12:18 ` Daniel Colascione
2019-05-28 12:38 ` Michal Hocko
2019-05-28 12:10 ` Minchan Kim
2019-05-28 11:44 ` Minchan Kim
2019-05-28 11:51 ` Daniel Colascione
2019-05-28 12:06 ` Michal Hocko
2019-05-28 12:22 ` Minchan Kim
2019-05-28 11:28 ` Daniel Colascione
2019-05-21 15:33 ` Johannes Weiner
2019-05-22 1:50 ` Minchan Kim
2019-05-20 9:28 ` [RFC 0/7] introduce memory hinting API for external process Michal Hocko
[not found] ` <20190520164605.GA11665@cmpxchg.org>
[not found] ` <20190521043950.GJ10039@google.com>
2019-05-21 6:32 ` Michal Hocko
[not found] ` <20190521014452.GA6738@bombadil.infradead.org>
2019-05-21 6:34 ` Michal Hocko
2019-05-21 12:53 ` Shakeel Butt
[not found] ` <dbe801f0-4bbe-5f6e-9053-4b7deb38e235@arm.com>
[not found] ` <CAEe=Sxka3Q3vX+7aWUJGKicM+a9Px0rrusyL+5bB1w4ywF6N4Q@mail.gmail.com>
[not found] ` <1754d0ef-6756-d88b-f728-17b1fe5d5b07@arm.com>
2019-05-21 12:56 ` Shakeel Butt
2019-05-22 4:23 ` Brian Geffon
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