On Tue, May 13, 2003 at 01:58:07PM -0700, Paul E. McKenney wrote:

The vmtruncate() function shifts down by PAGE_CACHE_SHIFT, then
calls vmtruncate_list(), which deals in terms of PAGE_SHIFT
instead.  Currently, no harm done, since PAGE_CACHE_SHIFT and
PAGE_SHIFT are identical.  Some day they might not be, hence
this patch.
I also took the liberty of modifying a hand-coded "if" that
seems to optimize for files that are not mapped to instead
use unlikely().

pgoff describes a file offset in the same units used to map files
with (the size of an area covered by a PTE), which is PAGE_SIZE (in
mainline; elsewhere it's called MMUPAGE_SIZE and I had to fix this
already for my tree). When they differ this would lose the offset into
the PAGE_CACHE_SIZE-sized file page; hence, well-spotted.


-- wli
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