On 9/9/21 8:57 PM, Al Viro wrote: > On Thu, Sep 09, 2021 at 03:19:56PM -0600, Jens Axboe wrote: > >> Not sure how we'd do that, outside of stupid tricks like copy the >> iov_iter before we pass it down. But that's obviously not going to be >> very efficient. Hence we're left with having some way to reset/reexpand, >> even in the presence of someone having done truncate on it. > > "Obviously" why, exactly? It's not that large a structure; it's not > the optimal variant, but I'd like to see profiling data before assuming > that it'll cause noticable slowdowns. It's 48 bytes, and we have to do it upfront. That means we'd be doing it for _all_ requests, not just when we need to retry. As an example, current benchmarks are at ~4M read requests per core. That'd add ~200MB/sec of memory traffic just doing this copy. Besides, I think that's moot as there's a better way. -- Jens Axboe
