Re: [PATCH v7 2/5] arm: arm64: page_alloc: reduce unnecessary binary search in memblock_next_valid_pfn()

[Matthew Wilcox]

On Thu, Apr 05, 2018 at 01:04:35AM -0700, Jia He wrote:
> Commit b92df1de5d28 ("mm: page_alloc: skip over regions of invalid pfns
> where possible") optimized the loop in memmap_init_zone(). But there is
> still some room for improvement. E.g. if pfn and pfn+1 are in the same
> memblock region, we can simply pfn++ instead of doing the binary search
> in memblock_next_valid_pfn.

Sure, but I bet if we are >end_pfn, we're almost certainly going to the
start_pfn of the next block, so why not test that as well?

> +     /* fast path, return pfn+1 if next pfn is in the same region */
> +     if (early_region_idx != -1) {
> +             start_pfn = PFN_DOWN(regions[early_region_idx].base);
> +             end_pfn = PFN_DOWN(regions[early_region_idx].base +
> +                             regions[early_region_idx].size);
> +
> +             if (pfn >= start_pfn && pfn < end_pfn)
> +                     return pfn;

                early_region_idx++;
                start_pfn = PFN_DOWN(regions[early_region_idx].base);
                if (pfn >= end_pfn && pfn <= start_pfn)
                        return start_pfn;
> +     }