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From: Minchan Kim <minchan@kernel.org>
To: Michal Hocko <mhocko@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 7/7] mm: madvise support MADV_ANONYMOUS_FILTER and MADV_FILE_FILTER
Date: Tue, 28 May 2019 21:22:07 +0900
Message-ID: <20190528122207.GD30365@google.com> (raw)
In-Reply-To: <20190528120614.GB1658@dhcp22.suse.cz>

On Tue, May 28, 2019 at 02:06:14PM +0200, Michal Hocko wrote:
> On Tue 28-05-19 20:44:36, Minchan Kim wrote:
> > On Tue, May 28, 2019 at 01:28:40PM +0200, Michal Hocko wrote:
> > > On Tue 28-05-19 20:12:08, Minchan Kim wrote:
> > > > On Tue, May 28, 2019 at 12:41:17PM +0200, Michal Hocko wrote:
> > > > > On Tue 28-05-19 19:32:56, Minchan Kim wrote:
> > > > > > On Tue, May 28, 2019 at 11:08:21AM +0200, Michal Hocko wrote:
> > > > > > > On Tue 28-05-19 17:49:27, Minchan Kim wrote:
> > > > > > > > On Tue, May 28, 2019 at 01:31:13AM -0700, Daniel Colascione wrote:
> > > > > > > > > On Tue, May 28, 2019 at 1:14 AM Minchan Kim <minchan@kernel.org> wrote:
> > > > > > > > > > if we went with the per vma fd approach then you would get this
> > > > > > > > > > > feature automatically because map_files would refer to file backed
> > > > > > > > > > > mappings while map_anon could refer only to anonymous mappings.
> > > > > > > > > >
> > > > > > > > > > The reason to add such filter option is to avoid the parsing overhead
> > > > > > > > > > so map_anon wouldn't be helpful.
> > > > > > > > > 
> > > > > > > > > Without chiming on whether the filter option is a good idea, I'd like
> > > > > > > > > to suggest that providing an efficient binary interfaces for pulling
> > > > > > > > > memory map information out of processes.  Some single-system-call
> > > > > > > > > method for retrieving a binary snapshot of a process's address space
> > > > > > > > > complete with attributes (selectable, like statx?) for each VMA would
> > > > > > > > > reduce complexity and increase performance in a variety of areas,
> > > > > > > > > e.g., Android memory map debugging commands.
> > > > > > > > 
> > > > > > > > I agree it's the best we can get *generally*.
> > > > > > > > Michal, any opinion?
> > > > > > > 
> > > > > > > I am not really sure this is directly related. I think the primary
> > > > > > > question that we have to sort out first is whether we want to have
> > > > > > > the remote madvise call process or vma fd based. This is an important
> > > > > > > distinction wrt. usability. I have only seen pid vs. pidfd discussions
> > > > > > > so far unfortunately.
> > > > > > 
> > > > > > With current usecase, it's per-process API with distinguishable anon/file
> > > > > > but thought it could be easily extended later for each address range
> > > > > > operation as userspace getting smarter with more information.
> > > > > 
> > > > > Never design user API based on a single usecase, please. The "easily
> > > > > extended" part is by far not clear to me TBH. As I've already mentioned
> > > > > several times, the synchronization model has to be thought through
> > > > > carefuly before a remote process address range operation can be
> > > > > implemented.
> > > > 
> > > > I agree with you that we shouldn't design API on single usecase but what
> > > > you are concerning is actually not our usecase because we are resilient
> > > > with the race since MADV_COLD|PAGEOUT is not destruptive.
> > > > Actually, many hints are already racy in that the upcoming pattern would
> > > > be different with the behavior you thought at the moment.
> > > 
> > > How come they are racy wrt address ranges? You would have to be in
> > > multithreaded environment and then the onus of synchronization is on
> > > threads. That model is quite clear. But we are talking about separate
> > 
> > Think about MADV_FREE. Allocator would think the chunk is worth to mark
> > "freeable" but soon, user of the allocator asked the chunk - ie, it's not
> > freeable any longer once user start to use it.
> 
> That is not a race in the address space, right. The underlying object
> hasn't changed. It has been declared as freeable and since that moment
> nobody can rely on the content because it might have been discarded.
> Or put simply, the content is undefined. It is responsibility of the
> madvise caller to make sure that the object is not in active use while
> it is marking it.
> 
> > My point is that kinds of *hints* are always racy so any synchronization
> > couldn't help a lot. That's why I want to restrict hints process_madvise
> > supports as such kinds of non-destruptive one at next respin.
> 
> I agree that a non-destructive operations are safer against paralel
> modifications because you just get a annoying and unexpected latency at
> worst case. But we should discuss whether this assumption is sufficient
> for further development. I am pretty sure once we open remote madvise
> people will find usecases for destructive operations or even new madvise
> modes we haven't heard of. What then?

I support Daniel's vma seq number approach for the future plan.


  reply index

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 [this message]
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
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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