Subject: Re: [Question] New mmap64 syscall?
To: Yury Norov <ynorov@caviumnetworks.com>
References: <20161206185440.GA4654@yury-N73SV>
 <f544bcc3-8aae-1bd0-b744-9964fc038a51@redhat.com>
 <20161207154811.GA15248@yury-N73SV>
Cc: libc-alpha@sourceware.org, linux-arch@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Catalin Marinas <catalin.marinas@arm.com>, szabolcs.nagy@arm.com,
        heiko.carstens@de.ibm.com, cmetcalf@ezchip.com,
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        zhouchengming1@huawei.com, Prasun.Kapoor@caviumnetworks.com,
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        linyongting@huawei.com, klimov.linux@gmail.com, broonie@kernel.org,
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        christoph.muellner@theobroma-systems.com
From: Florian Weimer <fweimer@redhat.com>
Message-ID: <14981df2-b120-17c3-a5a8-5cbbd2008c4f@redhat.com>
Date: Thu, 8 Dec 2016 16:47:34 +0100
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On 12/07/2016 04:48 PM, Yury Norov wrote:
> On Wed, Dec 07, 2016 at 02:23:55PM +0100, Florian Weimer wrote:
>> On 12/06/2016 07:54 PM, Yury Norov wrote:
>>> 3. Introduce new mmap64() syscall like this:
>>> sys_mmap64(void *addr, size_t len, int prot, int flags, int fd, struct off_pair *off);
>>> (The pointer here because otherwise we have 7 args, if simply pass off_hi and
>>> off_lo in registers.)
>>
>> I would prefer a batched mmap/munmap/mremap/mprotect/madvise interface, so
>> that VM changes can be coalesced and the output reduced.  This interface
>> could then be used to implement mmap on 32-bit architectures as well because
>> the offset restrictions would not apply there.
>
> Hi Florian,
>
> I frankly don't understand what you mean, All syscalls you mentioned
> doesn't take off_t or other 64-bit arguments. 'VM changes' - virtual
> memory? If so, I don't see any changes in VM with this approach, just
> correct handling of big offsets.

What I was trying to suggest is a completely different interface which 
is not subject to register size constraints and which has been requested 
before (a mechanism for batching mm updates).

Thanks,
Florian