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From:   Nathan Hjelm <hjelmn@me.com>
Message-id: <B9A6330F-48FE-4260-A505-3FF043874F0F@me.com>
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Subject: Re: [OMPI devel] [PATCH v5 0/4] vm: add a syscall to map a process
 memory into a pipe
Date:   Mon, 26 Feb 2018 09:38:19 -0700
In-reply-to: <3122ec5a-7f73-f6b4-33ea-8c10ef32e5b0@virtuozzo.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Mike Rapoport <rppt@linux.vnet.ibm.com>,
        Andrei Vagin <avagin@openvz.org>,
        Arnd Bergmann <arnd@arndb.de>, Jann Horn <jannh@google.com>,
        rr-dev@mozilla.org, linux-api@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Josh Triplett <josh@joshtriplett.org>, criu@openvz.org,
        linux-mm@kvack.org, Greg KH <gregkh@linuxfoundation.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>, gdb@sourceware.org,
        linux-fsdevel@vger.kernel.org,
        Thomas Gleixner <tglx@linutronix.de>,
        Michael Kerrisk <mtk.manpages@gmail.com>
To:     Open MPI Developers <devel@lists.open-mpi.org>
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 <20180220164406.3ec34509376f16841dc66e34@linux-foundation.org>
 <3122ec5a-7f73-f6b4-33ea-8c10ef32e5b0@virtuozzo.com>
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All MPI implementations have support for using CMA to transfer data =
between local processes. The performance is fairly good (not as good as =
XPMEM) but the interface limits what we can do with to remote process =
memory (no atomics). I have not heard about this new proposal. What is =
the benefit of the proposed calls over the existing calls?

-Nathan

> On Feb 26, 2018, at 2:02 AM, Pavel Emelyanov <xemul@virtuozzo.com> =
wrote:
>=20
> On 02/21/2018 03:44 AM, Andrew Morton wrote:
>> On Tue,  9 Jan 2018 08:30:49 +0200 Mike Rapoport =
<rppt@linux.vnet.ibm.com> wrote:
>>=20
>>> This patches introduces new process_vmsplice system call that =
combines
>>> functionality of process_vm_read and vmsplice.
>>=20
>> All seems fairly strightforward.  The big question is: do we know =
that
>> people will actually use this, and get sufficient value from it to
>> justify its addition?
>=20
> Yes, that's what bothers us a lot too :) I've tried to start with =
finding out if anyone
> used the sys_read/write_process_vm() calls, but failed :( Does anybody =
know how popular
> these syscalls are? If its users operate on big amount of memory, they =
could benefit from
> the proposed splice extension.
>=20
> -- Pavel
> _______________________________________________
> devel mailing list
> devel@lists.open-mpi.org
> https://lists.open-mpi.org/mailman/listinfo/devel


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