On Wed, Oct 28, 2020 at 05:05:08PM +0000, David Howells wrote:
> Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
>
> > > +{
> > > + 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.
>
> Hmmm - actually, I want a shift size, not a number of bytes as I divide by it
> twice in afs_page_dirty().
__AFS_PAGE_PRIV_MASK is a constant though. If your compiler can't
optimise a divide-by-a-constant-power-of-two into a shift-by-a-constant (*),
it's time to get yourself a new compiler.
(*) assuming that's faster on the CPU it's targetting.
