On Fri, 15 Feb 2008 16:47:19 -0800 Christoph Lameter [off-list ref] wrote:

V2->V3:
- Use "mapping" instead of "a" as the address space parameter

We use the macros PAGE_CACHE_SIZE PAGE_CACHE_SHIFT PAGE_CACHE_MASK
and PAGE_CACHE_ALIGN in various places in the kernel. Many times
common operations like calculating the offset or the index are coded
using shifts and adds. This patch provides inline functions to
get the calculations accomplished without having to explicitly
shift and add constants.

All functions take an address_space pointer. The address space pointer
will be used in the future to eventually support a variable size
page cache. Information reachable via the mapping may then determine
page size.

New function                    Related base page constant
====================================================================
page_cache_shift(a)             PAGE_CACHE_SHIFT
page_cache_size(a)              PAGE_CACHE_SIZE
page_cache_mask(a)              PAGE_CACHE_MASK
page_cache_index(a, pos)        Calculate page number from position
page_cache_next(addr, pos)      Page number of next page
page_cache_offset(a, pos)       Calculate offset into a page
page_cache_pos(a, index, offset)
                                Form position based on page number
                                and an offset.

These sort-of look OK as cleanups and avoidance of accidents.

But the interfaces which they use (passing and address_space) are quite
pointless unless we implement variable page size per address_space.  And as
the chances of that ever happening seem pretty damn small, these changes
are just obfuscation which make the code harder to read and which
pointlessly churn the codebase.

So I'm inclined to drop these patches.

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