Messages in this thread | | | Date | Tue, 25 Feb 2014 20:46:49 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2] mm: per-thread vma caching |
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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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