On Tue, Jul 24, 2007 at 12:32:15PM +0800, Fengguang Wu wrote:
> On Mon, Jul 23, 2007 at 08:55:35PM -0700, Andrew Morton wrote:
> > On Tue, 24 Jul 2007 10:00:12 +0800 Fengguang Wu <[EMAIL PROTECTED]> wrote:
> >
> > > @@ -342,11 +342,9 @@ ondemand_readahead(struct address_space
> > > bool hit_readahead_marker, pgoff_t offset,
> > > unsigned long req_size)
> > > {
> > > - int max; /* max readahead pages */
> > > - int sequential;
> > > -
> > > - max = ra->ra_pages;
> > > - sequential = (offset - ra->prev_index <= 1UL) || (req_size > max);
> > > + int max = ra->ra_pages; /* max readahead pages */
> > > + pgoff_t prev_offset;
> > > + int sequential;
> > >
> > > /*
> > > * It's the expected callback offset, assume sequential access.
> > > @@ -360,6 +358,9 @@ ondemand_readahead(struct address_space
> > > goto readit;
> > > }
> > >
> > > + prev_offset = ra->prev_pos >> PAGE_CACHE_SHIFT;
> > > + sequential = offset - prev_offset <= 1UL || req_size > max;
> >
> > It's a bit pointless using an opaque type for prev_offset here, and then
> > encoding the knowledge that it is implemented as "unsigned long".
> >
> > It's a minor thing, but perhaps just "<= 1" would make more sense here.
>
> Yeah, "<= 1" is OK. But the expression still requires pgoff_t to be
> 'unsigned' to work correctly.
>
> So what about "<= 1U"?
I wrote a test case and find that if pgoff_t is 'signed long',
"<= 1U" still yields the wrong result. Only "<= 1UL" does the trick :(
-
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