On 8/5/22 07:22, David Hildenbrand wrote: >> A list that sits besides the existing free_area, contains only >=pageblock >> order sizes of unaccepted pages (no migratetype distinguished) and we tap >> into it approximately before __rmqueue_fallback()? There would be some >> trickery around releasing zone-lock for doing accept_memory(), but should be >> manageable. >> > Just curious, do we have a microbenchmark that is able to reveal the > impact of such code changes before we start worrying? Nope. I went looking to see if I could find any impact. I think Kirill did too. Too bad that effort didn't make it into the changelog yet. The merging check at least is just checking a field in a cache-hot 'struct page'. The common case is probably three instructions: load to a register check the bit jump if not set It adds a wee bit of icache pressure, but it's also the kind of thing that should be a piece of cake for the branch predictors. That dynamic check could easily be wrapped by a static branch. But, that first requires more code to go dig in the nooks and crannies of the page allocator to make sure *ALL* pages are accepted.
