Re: [PATCH] remove 2TB block device limit

[Andrew Morton]

Peter Chubb wrote:
> 
> ...
> Christoph>  - why is the get_block block argument
> Christoph> a sector_t?  It presents a logical filesystem block which
> Christoph> usually is larger than the sector, not to mention that for
> Christoph> the usual blocksize == PAGE_SIZE case a ulong is enough as
> Christoph> that is 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.

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

This:

--- linux-2.5.15/include/linux/mm.h	Tue Apr 30 17:56:30 2002
+++ 25/include/linux/mm.h	Mon May 13 19:08:21 2002
@@ -148,7 +148,7 @@ struct vm_operations_struct {
 typedef struct page {
 	struct list_head list;		/* ->mapping has some page lists. */
 	struct address_space *mapping;	/* The inode (or ...) we belong to. */
-	unsigned long index;		/* Our offset within mapping. */
+	sector_t index;			/* Our offset within mapping. */
 	atomic_t count;			/* Usage count, see below. */
 	unsigned long flags;		/* atomic flags, some possibly
 					   updated asynchronously */

looks rather silly, no?

-