Matthew Wilcox <wi...@infradead.org> wrote:
> > +static inline unsigned int afs_page_dirty_resolution(void)
>
> I've been using size_t for offsets within a struct page. I don't know
> that we'll ever support pages larger than 2GB (they're completely
> impractical with today's bus speeds), but I'd rather not be the one
> who has to track down all the uses of 'int' in the kernel in fifteen
> years time.
Going beyond 2G page size won't be fun and a lot of our APIs will break -
write_begin, write_end, invalidatepage to name a few.
It would probably require an analysis program to trace all the usages of such
information within the kernel.
> > +{
> > + if (PAGE_SIZE - 1 <= __AFS_PAGE_PRIV_MASK)
> > + return 1;
> > + else
> > + return PAGE_SIZE / (__AFS_PAGE_PRIV_MASK + 1);
>
> Could this be DIV_ROUND_UP(PAGE_SIZE, __AFS_PAGE_PRIV_MASK + 1); avoiding
> a conditional? I appreciate it's calculated at compile time today, but
> it'll be dynamic with THP.
That seems to work.
> > static inline unsigned int afs_page_dirty_to(unsigned long priv)
> > {
> > - return ((priv >> __AFS_PAGE_PRIV_SHIFT) & __AFS_PAGE_PRIV_MASK) + 1;
> > + unsigned int x = (priv >> __AFS_PAGE_PRIV_SHIFT) & __AFS_PAGE_PRIV_MASK;
> > +
> > + /* The upper bound is exclusive */
>
> I think you mean 'inclusive'.
The returned upper bound points immediately beyond the range. E.g. 0-0 is an
empty range. Changing that is way too big an overhaul outside the merge
window.
> > + return (x + 1) * afs_page_dirty_resolution();
> > }
> >
> > static inline unsigned long afs_page_dirty(unsigned int from, unsigned int
> > to)
> > {
> > + unsigned int res = afs_page_dirty_resolution();
> > + from /= res; /* Round down */
> > + to = (to + res - 1) / res; /* Round up */
> > return ((unsigned long)(to - 1) << __AFS_PAGE_PRIV_SHIFT) | from;
>
> Wouldn't it produce the same result to just round down? ie:
>
> to = (to - 1) / res;
> return ((unsigned long)to << __AFS_PAGE_PRIV_SHIFT) | from;
Actually, yes, because res/res==1, which I then subtract afterwards.
David
