From: Rich Felker <dalias@libc.org>
To: Andy Lutomirski <luto@amacapital.net>,
Andy Lutomirski <luto@kernel.org>,
Till Smejkal <till.smejkal@googlemail.com>,
Richard Henderson <rth@twiddle.net>,
Ivan Kokshaysky <ink@jurassic.park.msu.ru>,
Matt Turner <mattst88@gmail.com>,
Vineet Gupta <vgupta@synopsys.com>,
Russell King <linux@armlinux.org.uk>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will.deacon@arm.com>,
Steven Miao <realmz6@gmail.com>,
Richard Kuo <rkuo@codeaurora.org>,
Tony Luck <tony.luck@intel.com>,
Fenghua Yu <fenghua.yu@intel.com>,
James Hogan <james.hogan@imgtec.com>,
Ralf Baechle <ralf@linux-mips.org>,
"James E.J. Bottomley" <jejb@parisc-linux.org>,
Helge Deller <deller@gmx.de>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Michael Ellerman <mpe@ellerman.id.au>,
Martin Schwidefsky <schwidefsky@de.ibm.com>,
Heiko Carstens <heiko.carstens@de>
Subject: Re: [RFC PATCH 00/13] Introduce first class virtual address spaces
Date: Wed, 15 Mar 2017 15:47:23 -0400 [thread overview]
Message-ID: <20170315194723.GJ1693__14401.0103344501$1489607445$gmane$org@brightrain.aerifal.cx> (raw)
In-Reply-To: <20170315194447.scsf3fiwvf7z5gzc@arch-dev>
On Wed, Mar 15, 2017 at 12:44:47PM -0700, Till Smejkal wrote:
> On Wed, 15 Mar 2017, Andy Lutomirski wrote:
> > > One advantage of VAS segments is that they can be globally queried by user programs
> > > which means that VAS segments can be shared by applications that not necessarily have
> > > to be related. If I am not mistaken, MAP_SHARED of pure in memory data will only work
> > > if the tasks that share the memory region are related (aka. have a common parent that
> > > initialized the shared mapping). Otherwise, the shared mapping have to be backed by a
> > > file.
> >
> > What's wrong with memfd_create()?
> >
> > > VAS segments on the other side allow sharing of pure in memory data by
> > > arbitrary related tasks without the need of a file. This becomes especially
> > > interesting if one combines VAS segments with non-volatile memory since one can keep
> > > data structures in the NVM and still be able to share them between multiple tasks.
> >
> > What's wrong with regular mmap?
>
> I never wanted to say that there is something wrong with regular mmap. We just
> figured that with VAS segments you could remove the need to mmap your shared data but
> instead can keep everything purely in memory.
>
> Unfortunately, I am not at full speed with memfds. Is my understanding correct that
> if the last user of such a file descriptor closes it, the corresponding memory is
> freed? Accordingly, memfd cannot be used to keep data in memory while no program is
> currently using it, can it? To be able to do this you need again some representation
I have a name for application-allocated kernel resources that persist
without a process holding a reference to them or a node in the
filesystem: a bug. See: sysvipc.
Rich
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next prev parent reply other threads:[~2017-03-15 19:50 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-13 22:14 Till Smejkal
2017-03-13 22:14 ` [RFC PATCH 01/13] mm: Add mm_struct argument to 'mmap_region' Till Smejkal
2017-03-13 22:14 ` [RFC PATCH 02/13] mm: Add mm_struct argument to 'do_mmap' and 'do_mmap_pgoff' Till Smejkal
2017-03-13 22:14 ` [RFC PATCH 03/13] mm: Rename 'unmap_region' and add mm_struct argument Till Smejkal
2017-03-13 22:14 ` [RFC PATCH 04/13] mm: Add mm_struct argument to 'get_unmapped_area' and 'vm_unmapped_area' Till Smejkal
2017-03-13 22:14 ` [RFC PATCH 05/13] mm: Add mm_struct argument to 'mm_populate' and '__mm_populate' Till Smejkal
2017-03-13 22:14 ` [RFC PATCH 06/13] mm/mmap: Export 'vma_link' and 'find_vma_links' to mm subsystem Till Smejkal
2017-03-13 22:14 ` [RFC PATCH 07/13] kernel/fork: Split and export 'mm_alloc' and 'mm_init' Till Smejkal
2017-03-14 10:18 ` David Laight
2017-03-14 16:18 ` Till Smejkal
2017-03-13 22:14 ` [RFC PATCH 08/13] kernel/fork: Define explicitly which mm_struct to duplicate during fork Till Smejkal
2017-03-13 22:14 ` [RFC PATCH 09/13] mm/memory: Add function to one-to-one duplicate page ranges Till Smejkal
2017-03-13 22:14 ` [RFC PATCH 10/13] mm: Introduce first class virtual address spaces Till Smejkal
2017-03-13 23:52 ` Greg Kroah-Hartman
2017-03-14 0:24 ` Till Smejkal
2017-03-14 1:35 ` Vineet Gupta
2017-03-14 2:34 ` Till Smejkal
2017-03-13 22:14 ` [RFC PATCH 11/13] mm/vas: Introduce VAS segments - shareable address space regions Till Smejkal
2017-03-13 22:27 ` Matthew Wilcox
2017-03-13 22:45 ` Till Smejkal
2017-03-13 22:14 ` [RFC PATCH 12/13] mm/vas: Add lazy-attach support for first class virtual address spaces Till Smejkal
2017-03-13 22:14 ` [RFC PATCH 13/13] fs/proc: Add procfs " Till Smejkal
2017-03-14 0:18 ` [RFC PATCH 00/13] Introduce " Richard Henderson
2017-03-14 0:39 ` Till Smejkal
2017-03-14 1:02 ` Richard Henderson
2017-03-14 1:31 ` Till Smejkal
2017-03-14 0:58 ` Andy Lutomirski
2017-03-14 2:07 ` Till Smejkal
2017-03-14 5:37 ` Andy Lutomirski
2017-03-14 16:12 ` Till Smejkal
2017-03-14 19:53 ` Chris Metcalf
2017-03-14 21:14 ` Till Smejkal
2017-03-15 16:51 ` Andy Lutomirski
2017-03-15 16:51 ` Andy Lutomirski
2017-03-15 16:57 ` Matthew Wilcox
2017-03-15 19:44 ` Till Smejkal
2017-03-15 19:47 ` Rich Felker [this message]
2017-03-15 19:47 ` Rich Felker
2017-03-15 21:30 ` Till Smejkal
2017-03-15 20:06 ` Andy Lutomirski
2017-03-15 22:02 ` Till Smejkal
2017-03-15 22:09 ` Luck, Tony
2017-03-15 23:18 ` Till Smejkal
2017-03-16 8:21 ` Thomas Gleixner
2017-03-16 17:29 ` Till Smejkal
2017-03-16 17:42 ` Thomas Gleixner
2017-03-16 17:50 ` Till Smejkal
2017-03-15 20:06 ` Andy Lutomirski
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