Date: Thu, 25 May 1995 20:03:47 -0700 (PDT) From: "Rodney W. Grimes" <rgrimes@gndrsh.aac.dev.com> To: davidg@Root.COM Cc: bde@zeta.org.au, current@FreeBSD.org Subject: Re: newfs weirdness... Message-ID: <199505260303.UAA01726@gndrsh.aac.dev.com> In-Reply-To: <199505260130.SAA00562@corbin.Root.COM> from "David Greenman" at May 25, 95 06:30:46 pm
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>
> >FreeBSD only supports 63 bit file system offsets. Files larger than 2GB
> >and mmapping at offsets larger than 2GB are currently broken. mmapping
> >of objects larger than 4G cannot work with the current interfaces.
>
> Ummm, the filesystem layer supports 40 bit file system offsets (the
> amount of a blkno that can be stored in 31 bits). The VM system, however,
> is currently limited to 31 bit file offsets which is why it can't deal
> with files larger than 2GB. We're going to fix this limit in the VM system,
> however, for FreeBSD 2.2 to be 43 bits by changing the 'offset' to be a
^^^^^^
> page offset rather than a byte offset. Once we do this, the limit will be
^^^^^^^^^^ ^^^^^^^^^^^
> imposed by bugs in the FS that store blkno in an int (the limit will then
> be 40 bits == 1TB). If we fix the FS bugs, then the limit will again be
> imposed by the VM system at 43 bits (8TB). I think limits in the terabyte
> range will be adequate for the medium term.
You are starting to ``think'' Intel x86 archicture, page sizes will vary
from arch to arch, be very carefull when doing this or you will end up
doing it again for any platfrom that does not use a 4K page size. And
even if you do make it work right, the limit will vary with machine page
size, which IMHO, is not a very good solution :-(.
--
Rod Grimes rgrimes@gndrsh.aac.dev.com
Accurate Automation Company Custom computers for FreeBSD
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