linux-kernel - Re: [Question] New mmap64 syscall?

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Message-ID: <14981df2-b120-17c3-a5a8-5cbbd2008c4f@redhat.com>
Date:   Thu, 8 Dec 2016 16:47:34 +0100
From:   Florian Weimer <fweimer@...hat.com>
To:     Yury Norov <ynorov@...iumnetworks.com>
Cc:     libc-alpha@...rceware.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        szabolcs.nagy@....com, heiko.carstens@...ibm.com,
        cmetcalf@...hip.com, philipp.tomsich@...obroma-systems.com,
        joseph@...esourcery.com, zhouchengming1@...wei.com,
        Prasun.Kapoor@...iumnetworks.com, agraf@...e.de,
        geert@...ux-m68k.org, kilobyte@...band.pl,
        manuel.montezelo@...il.com, arnd@...db.de, pinskia@...il.com,
        linyongting@...wei.com, klimov.linux@...il.com, broonie@...nel.org,
        bamvor.zhangjian@...wei.com, linux-arm-kernel@...ts.infradead.org,
        maxim.kuvyrkov@...aro.org, Nathan_Lynch@...tor.com,
        schwidefsky@...ibm.com, davem@...emloft.net,
        christoph.muellner@...obroma-systems.com
Subject: Re: [Question] New mmap64 syscall?

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