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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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