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But maybe there are some low-hanging fruits to >> optimize? Finding the main cause for the added overhead would be >> interesting. Agreed, knowing the exact root cause would be really nice. > Can you compare uffdio_copy() when using anonymous memory vs. shmem? > That's likely the best we could currently achieve with guest_memfd. Yeah, I was doing that too. It was about ~28% slower in my setup, while with guest_memfd it was ~34% slower. The variance of the data was quite high so the difference may well be just noise. In other words, I'd be much happier if we could bring guest_memfd (or even shmem) performance closer to the anon/private than if we just equalised guest_memfd with shmem (which are probably already pretty close). > There is the tools/testing/selftests/mm/uffd-stress benchmark, not sure > if that is of any help; it SEGFAULTS for me right now with a (likely) > division by 0. Thanks for the pointer, will take a look! > Cheers, > > David / dhildenb >