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resource: avoid unnecessary resource tree walking in __region_interse…
…cts() Currently, if __region_intersects() finds any overlapped but unmatched resource, it walks the descendant resource tree to check for overlapped and matched descendant resources using for_each_resource(). However, in current kernel, for_each_resource() iterates not only the descendant tree, but also subsequent sibling trees in certain scenarios. While this doesn't introduce bugs, it makes code hard to be understood and potentially inefficient. So, the patch revises next_resource() and for_each_resource() and makes for_each_resource() traverse the subtree under the specified subtree root only. Test shows that this avoids unnecessary resource tree walking in __region_intersects(). For the example resource tree as follows, X | A----D----E | B--C if 'A' is the overlapped but unmatched resource, original kernel iterates 'B', 'C', 'D', 'E' when it walks the descendant tree. While the patched kernel iterates only 'B', 'C'. Thanks David Hildenbrand for providing a good resource tree example. Link: https://lkml.kernel.org/r/20241029122735.79164-1-ying.huang@intel.com Signed-off-by: "Huang, Ying" <ying.huang@intel.com> Acked-by: Dan Williams <dan.j.williams@intel.com> Cc: David Hildenbrand <david@redhat.com> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Jonathan Cameron <jonathan.cameron@huawei.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Cc: Bjorn Helgaas <bhelgaas@google.com> Cc: Baoquan He <bhe@redhat.com> Cc: Dave Jiang <dave.jiang@intel.com> Cc: Alison Schofield <alison.schofield@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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