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

From: Jia He
Date: Thu Apr 05 2018 - 08:44:34 EST

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;
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?