On Tue, Feb 25, 2014 at 10:37:34AM -0800, Davidlohr Bueso wrote:
> On Tue, 2014-02-25 at 19:35 +0100, Peter Zijlstra wrote:
> > On Tue, Feb 25, 2014 at 10:16:46AM -0800, Davidlohr Bueso wrote:
> > > +void vmacache_update(struct mm_struct *mm, unsigned long addr,
> > > + struct vm_area_struct *newvma)
> > > +{
> > > + /*
> > > + * Hash based on the page number. Provides a good
> > > + * hit rate for workloads with good locality and
> > > + * those with random accesses as well.
> > > + */
> > > + int idx = (addr >> PAGE_SHIFT) & 3;
> >
> > % VMACACHE_SIZE
> >
> > perhaps? GCC should turn that into a mask for all sensible values I
> > would think.
> >
> > Barring that I think something like:
> >
> > #define VMACACHE_BITS 2
> > #define VMACACHE_SIZE (1U << VMACACHE_BITS)
> > #define VMACACHE_MASK (VMACACHE_SIZE - 1)
>
> Hmm all that seems like an overkill.
If GCC does the right thing with % VMACACHE_SIZE it gets rid of an ugly
constant. But the 3 VMACACHE_* things are 'better' in that its
impossible to set VMACACHE_SIZE to silly values.
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