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    SubjectRe: [PATCH v7 2/5] arm: arm64: page_alloc: reduce unnecessary binary search in memblock_next_valid_pfn()
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    On 4/5/2018 7:34 PM, Matthew Wilcox Wrote:
    > 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;
    Thanks, thus the binary search in next step can be discarded?

    --
    Cheers,
    Jia

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