Re: [PATCH v2] mm: per-thread vma caching

[Davidlohr Bueso]

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.

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