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

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Date:   Sat, 10 Dec 2016 10:21:30 +0100
From:   Pavel Machek <pavel@....cz>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     "Dr. Philipp Tomsich" <philipp.tomsich@...obroma-systems.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Yury Norov <ynorov@...iumnetworks.com>,
        libc-alpha@...rceware.org, linux-arch@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>, szabolcs.nagy@....com,
        heiko.carstens@...ibm.com, cmetcalf@...hip.com,
        "Joseph S. Myers" <joseph@...esourcery.com>,
        zhouchengming1@...wei.com,
        "Kapoor, Prasun" <Prasun.Kapoor@...iumnetworks.com>,
        Alexander Graf <agraf@...e.de>, geert@...ux-m68k.org,
        kilobyte@...band.pl, manuel.montezelo@...il.com,
        Andrew Pinski <pinskia@...il.com>, linyongting@...wei.com,
        Alexey Klimov <klimov.linux@...il.com>, broonie@...nel.org,
        "Zhangjian (Bamvor)" <bamvor.zhangjian@...wei.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Maxim Kuvyrkov <maxim.kuvyrkov@...aro.org>,
        Nathan Lynch <Nathan_Lynch@...tor.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        davem@...emloft.net, christoph.muellner@...obroma-systems.com
Subject: Re: [Question] New mmap64 syscall?

On Sat 2016-12-10 10:10:01, Pavel Machek wrote:
> Hi!
> 
> > > Most of these advantages should eventually go away, when struct-reorg makes
> > > it way into the compiler. That said, it’s a marginal (but real) improvement for a
> > > subset of SPEC.
> > > 
> > > In the real world, the importance of ILP32 as an aid to transition legacy code
> > > that is not 64bit clean… and this should drive the ILP32 discussion. That we
> > > get a boost in our SPEC scores is just a nice extra that we get from it 
> > 
> > To bring this back from the philosophical questions of ABI design
> > to the specific point of what file offset width you want for mmap()
> > on 32-bit architectures.
> > 
> > For all I can tell, using mmap() to access a file that is many thousand
> > times larger than your virtual address space is completely crazy.
> 
> Dunno. Wanting to mmap part of a partition does not seem too crazy... I'm pretty
> sure there's some tool out there that uses mmap(), just because mmap() was nicer
> to use then read(). And when the partition is big, the offset may be big.

Actually, if I wrote something like jpegrecover, I'd use mmap() for that (because
otherwise I'd be keeping copy of disk in anonymous memory, increasing memory pressure).

jpegrecover definitely makes sense on partitions...

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html