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From: Christian Brauner <christian@brauner.io>
To: Daniel Colascione <dancol@google.com>
Cc: Minchan Kim <minchan@kernel.org>,
	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>,
	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>, Jann Horn <jannh@google.com>
Subject: Re: [RFC 0/7] introduce memory hinting API for external process
Date: Wed, 22 May 2019 16:52:18 +0200
Message-ID: <20190522145216.jkimuudoxi6pder2@brauner.io> (raw)
In-Reply-To: <CAKOZueupb10vmm-bmL0j_b__qsC9ZrzhzHgpGhwPVUrfX0X-Og@mail.gmail.com>

On Wed, May 22, 2019 at 06:16:35AM -0700, Daniel Colascione wrote:
> On Wed, May 22, 2019 at 1:22 AM Christian Brauner <christian@brauner.io> wrote:
> >
> > On Wed, May 22, 2019 at 7:12 AM Daniel Colascione <dancol@google.com> wrote:
> > >
> > > On Tue, May 21, 2019 at 4:39 AM Christian Brauner <christian@brauner.io> wrote:
> > > >
> > > > On Tue, May 21, 2019 at 01:30:29PM +0200, Christian Brauner wrote:
> > > > > On Tue, May 21, 2019 at 08:05:52PM +0900, Minchan Kim wrote:
> > > > > > On Tue, May 21, 2019 at 10:42:00AM +0200, Christian Brauner wrote:
> > > > > > > On Mon, May 20, 2019 at 12:52:47PM +0900, Minchan Kim wrote:
> > > > > > > > - Background
> > > > > > > >
> > > > > > > > The Android terminology used for forking a new process and starting an app
> > > > > > > > from scratch is a cold start, while resuming an existing app is a hot start.
> > > > > > > > While we continually try to improve the performance of cold starts, hot
> > > > > > > > starts will always be significantly less power hungry as well as faster so
> > > > > > > > we are trying to make hot start more likely than cold start.
> > > > > > > >
> > > > > > > > To increase hot start, Android userspace manages the order that apps should
> > > > > > > > be killed in a process called ActivityManagerService. ActivityManagerService
> > > > > > > > tracks every Android app or service that the user could be interacting with
> > > > > > > > at any time and translates that into a ranked list for lmkd(low memory
> > > > > > > > killer daemon). They are likely to be killed by lmkd if the system has to
> > > > > > > > reclaim memory. In that sense they are similar to entries in any other cache.
> > > > > > > > Those apps are kept alive for opportunistic performance improvements but
> > > > > > > > those performance improvements will vary based on the memory requirements of
> > > > > > > > individual workloads.
> > > > > > > >
> > > > > > > > - Problem
> > > > > > > >
> > > > > > > > Naturally, cached apps were dominant consumers of memory on the system.
> > > > > > > > However, they were not significant consumers of swap even though they are
> > > > > > > > good candidate for swap. Under investigation, swapping out only begins
> > > > > > > > once the low zone watermark is hit and kswapd wakes up, but the overall
> > > > > > > > allocation rate in the system might trip lmkd thresholds and cause a cached
> > > > > > > > process to be killed(we measured performance swapping out vs. zapping the
> > > > > > > > memory by killing a process. Unsurprisingly, zapping is 10x times faster
> > > > > > > > even though we use zram which is much faster than real storage) so kill
> > > > > > > > from lmkd will often satisfy the high zone watermark, resulting in very
> > > > > > > > few pages actually being moved to swap.
> > > > > > > >
> > > > > > > > - Approach
> > > > > > > >
> > > > > > > > The approach we chose was to use a new interface to allow userspace to
> > > > > > > > proactively reclaim entire processes by leveraging platform information.
> > > > > > > > This allowed us to bypass the inaccuracy of the kernel’s LRUs for pages
> > > > > > > > that are known to be cold from userspace and to avoid races with lmkd
> > > > > > > > by reclaiming apps as soon as they entered the cached state. Additionally,
> > > > > > > > it could provide many chances for platform to use much information to
> > > > > > > > optimize memory efficiency.
> > > > > > > >
> > > > > > > > IMHO we should spell it out that this patchset complements MADV_WONTNEED
> > > > > > > > and MADV_FREE by adding non-destructive ways to gain some free memory
> > > > > > > > space. MADV_COLD is similar to MADV_WONTNEED in a way that it hints the
> > > > > > > > kernel that memory region is not currently needed and should be reclaimed
> > > > > > > > immediately; MADV_COOL is similar to MADV_FREE in a way that it hints the
> > > > > > > > kernel that memory region is not currently needed and should be reclaimed
> > > > > > > > when memory pressure rises.
> > > > > > > >
> > > > > > > > To achieve the goal, the patchset introduce two new options for madvise.
> > > > > > > > One is MADV_COOL which will deactive activated pages and the other is
> > > > > > > > MADV_COLD which will reclaim private pages instantly. These new options
> > > > > > > > complement MADV_DONTNEED and MADV_FREE by adding non-destructive ways to
> > > > > > > > gain some free memory space. MADV_COLD is similar to MADV_DONTNEED in a way
> > > > > > > > that it hints the kernel that memory region is not currently needed and
> > > > > > > > should be reclaimed immediately; MADV_COOL is similar to MADV_FREE in a way
> > > > > > > > that it hints the kernel that memory region is not currently needed and
> > > > > > > > should be reclaimed when memory pressure rises.
> > > > > > > >
> > > > > > > > This approach is similar in spirit to madvise(MADV_WONTNEED), but the
> > > > > > > > information required to make the reclaim decision is not known to the app.
> > > > > > > > Instead, it is known to a centralized userspace daemon, and that daemon
> > > > > > > > must be able to initiate reclaim on its own without any app involvement.
> > > > > > > > To solve the concern, this patch introduces new syscall -
> > > > > > > >
> > > > > > > >         struct pr_madvise_param {
> > > > > > > >                 int size;
> > > > > > > >                 const struct iovec *vec;
> > > > > > > >         }
> > > > > > > >
> > > > > > > >         int process_madvise(int pidfd, ssize_t nr_elem, int *behavior,
> > > > > > > >                                 struct pr_madvise_param *restuls,
> > > > > > > >                                 struct pr_madvise_param *ranges,
> > > > > > > >                                 unsigned long flags);
> > > > > > > >
> > > > > > > > The syscall get pidfd to give hints to external process and provides
> > > > > > > > pair of result/ranges vector arguments so that it could give several
> > > > > > > > hints to each address range all at once.
> > > > > > > >
> > > > > > > > I guess others have different ideas about the naming of syscall and options
> > > > > > > > so feel free to suggest better naming.
> > > > > > >
> > > > > > > Yes, all new syscalls making use of pidfds should be named
> > > > > > > pidfd_<action>. So please make this pidfd_madvise.
> > > > > >
> > > > > > I don't have any particular preference but just wondering why pidfd is
> > > > > > so special to have it as prefix of system call name.
> > > > >
> > > > > It's a whole new API to address processes. We already have
> > > > > clone(CLONE_PIDFD) and pidfd_send_signal() as you have seen since you
> > > > > exported pidfd_to_pid(). And we're going to have pidfd_open(). Your
> > > > > syscall works only with pidfds so it's tied to this api as well so it
> > > > > should follow the naming scheme. This also makes life easier for
> > > > > userspace and is consistent.
> > > >
> > > > This is at least my reasoning. I'm not going to make this a whole big
> > > > pedantic argument. If people have really strong feelings about not using
> > > > this prefix then fine. But if syscalls can be grouped together and have
> > > > consistent naming this is always a big plus.
> > >
> > > My hope has been that pidfd use becomes normalized enough that
> > > prefixing "pidfd_" to pidfd-accepting system calls becomes redundant.
> > > We write write(), not fd_write(), right? :-) pidfd_open() makes sense
> > > because the primary purpose of this system call is to operate on a
> > > pidfd, but I think process_madvise() is fine.
> >
> > This madvise syscall just operates on pidfds. It would make sense to
> > name it process_madvise() if were to operate both on pid_t and int pidfd.
> 
> The name of the function ought to encode its purpose, not its
> signature. The system call under discussion operates on processes and
> so should be called "process_madvise". That this system call happens
> to accept a pidfd to identify the process on which it operates is not
> its most interesting aspect of the system call. The argument type
> isn't important enough to spotlight in the permanent name of an API.
> Pidfds are novel now, but they won't be novel in the future.

I'm not going to go into yet another long argument. I prefer pidfd_*.
It's tied to the api, transparent for userspace, and disambiguates it
from process_vm_{read,write}v that both take a pid_t.


  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
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 [this message]
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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