Re: [PATCH 09/25] ia64: Preemptible mmu_gather

From: Tony Luck
Date: Tue Jan 25 2011 - 15:13:03 EST

On Tue, Jan 25, 2011 at 9:31 AM, Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> wrote:
>  struct mmu_gather {
>        struct mm_struct        *mm;
>        unsigned int            nr;             /* == ~0U => fast mode */
> +       unsigned int            max;
>        unsigned char           fullmm;         /* non-zero means full mm flush */
>        unsigned char           need_flush;     /* really unmapped some PTEs? */
>        unsigned long           start_addr;
>        unsigned long           end_addr;
> -       struct page             *pages[FREE_PTE_NR];
> +       struct page             **pages;
> +       struct page             *local[8];
>  };

Overall it looks OK - builds, boots & runs too. One question about
the above bit ... why "8" elements in the local[] array? This ought to be
a #define, maybe with a comment explaining the significance. It doesn't
seem to fill out struct mmu_gather to some "nice" size. I can't think
of why batching 8 at a time (in the fallback cannot allocate **pages case)
is a good number. So is there some science to the choice, or did you
pluck 8 out of the air?


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