On Tue, Apr 12, 2022 at 06:57:57AM +0200, Christoph Hellwig wrote: > On Fri, Apr 08, 2022 at 11:08:29PM -0700, Hugh Dickins wrote: > > > > > > Either way I'd rather do this optimization in iov_iter_zero rather > > > than hiding it in tmpfs. > > > > Let's see what others say. I think we would all prefer clear_user() to be > > enhanced, and hack around it neither here in tmpfs nor in iov_iter_zero(). > > But that careful work won't get done by magic, nor by me. > > I agree with that. > > > And iov_iter_zero() has to deal with a wider range of possibilities, > > when pulling in cache lines of ZERO_PAGE(0) will be less advantageous, > > than in tmpfs doing a large dd - the case I'm aiming not to regress here > > (tmpfs has been copying ZERO_PAGE(0) like this for years). > > Maybe. OTOH I'd hate to have iov_iter_zero not used much because it > sucks too much. > > So how can we entice someone with the right knowledge to implement a > decent clear_user for x86? Apparently that already happened, but it needs finishing up: https://lore.kernel.org/lkml/Yk9yBcj78mpXOOLL@xxxxxxxxx/
