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From: Minchan Kim <minchan@kernel.org>
To: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Tim Murray <timmurray@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-mm <linux-mm@kvack.org>, Michal Hocko <mhocko@suse.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Joel Fernandes <joel@joelfernandes.org>,
	Suren Baghdasaryan <surenb@google.com>,
	Daniel Colascione <dancol@google.com>,
	Shakeel Butt <shakeelb@google.com>,
	Sonny Rao <sonnyrao@google.com>,
	Brian Geffon <bgeffon@google.com>
Subject: Re: [RFC 0/7] introduce memory hinting API for external process
Date: Tue, 21 May 2019 14:14:51 +0900
Message-ID: <20190521051451.GL10039@google.com> (raw)
In-Reply-To: <1754d0ef-6756-d88b-f728-17b1fe5d5b07@arm.com>

On Tue, May 21, 2019 at 08:25:55AM +0530, Anshuman Khandual wrote:
> 
> 
> On 05/20/2019 10:29 PM, Tim Murray wrote:
> > On Sun, May 19, 2019 at 11:37 PM Anshuman Khandual
> > <anshuman.khandual@arm.com> wrote:
> >>
> >> Or Is the objective here is reduce the number of processes which get killed by
> >> lmkd by triggering swapping for the unused memory (user hinted) sooner so that
> >> they dont get picked by lmkd. Under utilization for zram hardware is a concern
> >> here as well ?
> > 
> > The objective is to avoid some instances of memory pressure by
> > proactively swapping pages that userspace knows to be cold before
> > those pages reach the end of the LRUs, which in turn can prevent some
> > apps from being killed by lmk/lmkd. As soon as Android userspace knows
> > that an application is not being used and is only resident to improve
> > performance if the user returns to that app, we can kick off
> > process_madvise on that process's pages (or some portion of those
> > pages) in a power-efficient way to reduce memory pressure long before
> > the system hits the free page watermark. This allows the system more
> > time to put pages into zram versus waiting for the watermark to
> > trigger kswapd, which decreases the likelihood that later memory
> > allocations will cause enough pressure to trigger a kill of one of
> > these apps.
> 
> So this opens up bit of LRU management to user space hints. Also because the app
> in itself wont know about the memory situation of the entire system, new system
> call needs to be called from an external process.

That's why process_madvise is introduced here.

> 
> > 
> >> Swapping out memory into zram wont increase the latency for a hot start ? Or
> >> is it because as it will prevent a fresh cold start which anyway will be slower
> >> than a slow hot start. Just being curious.
> > 
> > First, not all swapped pages will be reloaded immediately once an app
> > is resumed. We've found that an app's working set post-process_madvise
> > is significantly smaller than what an app allocates when it first
> > launches (see the delta between pswpin and pswpout in Minchan's
> > results). Presumably because of this, faulting to fetch from zram does
> 
> pswpin      417613    1392647     975034     233.00
> pswpout    1274224    2661731    1387507     108.00
> 
> IIUC the swap-in ratio is way higher in comparison to that of swap out. Is that
> always the case ? Or it tend to swap out from an active area of the working set
> which faulted back again.

I think it's because apps are alive longer via reducing being killed
so turn into from pgpgin to swapin.

> 
> > not seem to introduce a noticeable hot start penalty, not does it
> > cause an increase in performance problems later in the app's
> > lifecycle. I've measured with and without process_madvise, and the
> > differences are within our noise bounds. Second, because we're not
> 
> That is assuming that post process_madvise() working set for the application is
> always smaller. There is another challenge. The external process should ideally
> have the knowledge of active areas of the working set for an application in
> question for it to invoke process_madvise() correctly to prevent such scenarios.

There are several ways to detect workingset more accurately at the cost
of runtime. For example, with idle page tracking or clear_refs. Accuracy
is always trade-off of overhead for LRU aging.

> 
> > preemptively evicting file pages and only making them more likely to
> > be evicted when there's already memory pressure, we avoid the case
> > where we process_madvise an app then immediately return to the app and
> > reload all file pages in the working set even though there was no
> > intervening memory pressure. Our initial version of this work evicted
> 
> That would be the worst case scenario which should be avoided. Memory pressure
> must be a parameter before actually doing the swap out. But pages if know to be
> inactive/cold can be marked high priority to be swapped out.
> 
> > file pages preemptively and did cause a noticeable slowdown (~15%) for
> > that case; this patch set avoids that slowdown. Finally, the benefit
> > from avoiding cold starts is huge. The performance improvement from
> > having a hot start instead of a cold start ranges from 3x for very
> > small apps to 50x+ for larger apps like high-fidelity games.
> 
> Is there any other real world scenario apart from this app based ecosystem where
> user hinted LRU management might be helpful ? Just being curious. Thanks for the
> detailed explanation. I will continue looking into this series.


  reply index

Thread overview: 138+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-20  3:52 Minchan Kim
2019-05-20  3:52 ` [RFC 1/7] mm: introduce MADV_COOL Minchan Kim
2019-05-20  8:16   ` 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
2019-05-28  8:53   ` Hillf Danton
2019-05-28 10:58   ` Minchan Kim
2019-05-20  3:52 ` [RFC 2/7] mm: change PAGEREF_RECLAIM_CLEAN with PAGE_REFRECLAIM Minchan Kim
2019-05-20 16:50   ` Johannes Weiner
2019-05-20 22:57     ` Minchan Kim
2019-05-20  3:52 ` [RFC 3/7] mm: introduce MADV_COLD Minchan Kim
2019-05-20  8:27   ` Michal Hocko
2019-05-20 23:00     ` Minchan Kim
2019-05-21  6:08       ` Michal Hocko
2019-05-21  9:13         ` Minchan Kim
2019-05-28 14:54   ` Hillf Danton
2019-05-30  0:45   ` Minchan Kim
2019-05-20  3:52 ` [RFC 4/7] mm: factor out madvise's core functionality Minchan Kim
2019-05-20 14:26   ` Oleksandr Natalenko
2019-05-21  1:26     ` Minchan Kim
2019-05-21  6:36       ` Oleksandr Natalenko
2019-05-21  6:50         ` Michal Hocko
2019-05-21  7:06           ` Oleksandr Natalenko
2019-05-21 10:52             ` Minchan Kim
2019-05-21 11:00               ` Michal Hocko
2019-05-21 11:24                 ` Minchan Kim
2019-05-21 11:32                   ` Michal Hocko
2019-05-21 10:49         ` Minchan Kim
2019-05-21 10:55           ` Michal Hocko
2019-05-20  3:52 ` [RFC 5/7] mm: introduce external memory hinting API Minchan Kim
2019-05-20  9:18   ` Michal Hocko
2019-05-21  2:41     ` Minchan Kim
2019-05-21  6:17       ` Michal Hocko
2019-05-21 10:32         ` Minchan Kim
2019-05-21  9:01   ` Christian Brauner
2019-05-21 11:35     ` Minchan Kim
2019-05-21 11:51       ` Christian Brauner
2019-05-21 15:31   ` Oleg Nesterov
2019-05-27  7:43     ` Minchan Kim
2019-05-27 15:12       ` Oleg Nesterov
2019-05-27 23:33         ` Minchan Kim
2019-05-28  7:23           ` Michal Hocko
2019-05-29  3:41   ` Hillf Danton
2019-05-30  0:38   ` Minchan Kim
2019-05-20  3:52 ` [RFC 6/7] mm: extend process_madvise syscall to support vector arrary Minchan Kim
2019-05-20  9:22   ` 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
2019-05-30  8:02                       ` Minchan Kim
2019-05-30 16:19                         ` Daniel Colascione
2019-05-30 18:47                         ` Michal Hocko
2019-05-29  4:14   ` Hillf Danton
2019-05-30  0:35   ` Minchan Kim
2019-05-20  3:52 ` [RFC 7/7] mm: madvise support MADV_ANONYMOUS_FILTER and MADV_FILE_FILTER Minchan Kim
2019-05-20  9:28   ` 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
2019-05-29  4:36   ` Hillf Danton
2019-05-30  1:00   ` Minchan Kim
2019-05-20  6:37 ` [RFC 0/7] introduce memory hinting API for external process Anshuman Khandual
2019-05-20 16:59   ` Tim Murray
2019-05-21  2:55     ` Anshuman Khandual
2019-05-21  5:14       ` Minchan Kim [this message]
2019-05-21 10:34       ` Michal Hocko
2019-05-28 10:50         ` Anshuman Khandual
2019-05-21 12:56       ` Shakeel Butt
2019-05-22  4:15         ` Brian Geffon
2019-05-22  4:23         ` Brian Geffon
2019-05-20  9:28 ` Michal Hocko
2019-05-20 14:42 ` Oleksandr Natalenko
2019-05-21  2:56   ` Minchan Kim
2019-05-20 16:46 ` Johannes Weiner
2019-05-21  4:39   ` Minchan Kim
2019-05-21  6:32     ` Michal Hocko
2019-05-21  1:44 ` Matthew Wilcox
2019-05-21  5:01   ` Minchan Kim
2019-05-21  6:34   ` Michal Hocko
2019-05-21  8:42 ` Christian Brauner
2019-05-21 11:05   ` Minchan Kim
2019-05-21 11:30     ` Christian Brauner
2019-05-21 11:39       ` Christian Brauner
2019-05-22  5:11         ` Daniel Colascione
2019-05-22  8:22           ` Christian Brauner
2019-05-22 13:16             ` Daniel Colascione
2019-05-22 14:52               ` Christian Brauner
2019-05-22 15:17                 ` Daniel Colascione
2019-05-22 15:48                   ` Christian Brauner
2019-05-22 15:57                     ` Daniel Colascione
2019-05-22 16:01                       ` Christian Brauner
2019-05-22 16:01                         ` Daniel Colascione
2019-05-23 13:07                           ` Minchan Kim
2019-05-27  8:06                             ` Minchan Kim
2019-05-21 11:41       ` Minchan Kim
2019-05-21 12:04         ` Christian Brauner
2019-05-21 12:15           ` Oleksandr Natalenko
2019-05-21 12:53 ` Shakeel Butt

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