From: Daniel Colascione <dancol@google.com>
To: Christian Brauner <christian@brauner.io>
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: Tue, 21 May 2019 22:11:53 -0700 [thread overview]
Message-ID: <CAKOZuesjDcD3EM4PS7aO7yTa3KZ=FEzMP63MR0aEph4iW1NCYQ@mail.gmail.com> (raw)
In-Reply-To: <20190521113911.2rypoh7uniuri2bj@brauner.io>
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.
next prev parent reply other threads:[~2019-05-22 5:12 UTC|newest]
Thread overview: 138+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-20 3:52 [RFC 0/7] introduce memory hinting API for external process 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 [this message]
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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