Re: [PATCH] remove 2TB block device limit

[Peter Chubb <peter@chubb.wattle.id.au>]

>>>>> "Andrew" == Andrew Morton <akpm@zip.com.au> writes:

Andrew> Peter Chubb wrote:
>> ...
Christoph> - why is the get_block block argument a sector_t?  It
Christoph> presents a logical filesystem block which usually is larger
Christoph> than the sector, not to mention that for the usual
Christoph> blocksize == PAGE_SIZE case a ulong is enough as that is
Christoph> the same size the pagecache limit triggers.
>> For filesystems that *can* handle logical filesystem blocks beyond
>> the 2^32 limit (i.e., that use >32bit offsets in their on-disc
>> format), the get_block() argument has to be > 32bits long.  At the
>> moment that's only JFS and XFS, but reiserfs version 4 looks as if
>> it might go that way.  We'll need this especially when the
>> pagecache limit is gone.

Andrew> I think Christoph's point is that a pagecache index is not a
Andrew> sector number.  We agree that we need to plan for taking it to
Andrew> 64 bits, but it should be something different. Like
Andrew> pageindex_t, or whatever.


I'll let Christoph speak for himself, but my point is that
get_block() is an interface exported from the filesystem.  It should
be possible to specify any logical block number that the filesystem
supports.   That the current VM system on 32-bit machines will never
request a block beyond 2^32 is a (one-day-soon-to-be-removed) current
limitation. 

Peter C