* Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> [220825 21:06]: > On Thu, 25 Aug 2022 20:30:24 +0000 Liam Howlett <liam.howlett@xxxxxxxxxx> wrote: > > > Use the untagged_addr() instead of the address passed into the function. > > What are the runtime effects of this fix? Prior to my change to use the maple tree, the start address was changed before calling find_vma() with the untagged_addr() version of start. My first change recorded the tagged address and searched on the incorrect start location - which would have found the incorrect VMA. This fix will use the untagged_addr() as the start of the search as it was before I changed the code at all. Any penalty of calling untagged_addr() occurred regardless of the version that was used. The search of the maple tree would have also occurred in both versions - just at the wrong location before this fix. I expect that the execution time would be equal as the search on the tagged address would have either returned a VMA at start, or the VMA in the next slot in the maple tree node - probably immeasurably slower since the data is very likely already in the CPU cache, but I don't have hard data to say either way. I can look into a benchmark to measure the difference between both working versions, but I don't have an arm64 native target so it will be emulated.
