On Thu, Aug 08, 2024 at 04:35:05AM +0100, Al Viro wrote: > On Wed, Aug 07, 2024 at 08:06:31PM -0700, Linus Torvalds wrote: > > But release/acquire is the RightThing(tm), and the fact that alpha > > based its ordering on the bad old model is not really our problem. > > alpha would have fuckloads of full barriers simply from all those READ_ONCE() > in rcu reads... > > smp_rmb() is on the side that is much hotter - fd_install() vs. up to what, 25 calls > of expand_fdtable() per files_struct instance history in the worst possible case? > With rather big memcpy() done by those calls, at that... BTW, an alternative would be to have LSB of ->fdt (or ->fd, if we try to eliminate that extra dereference) for ->resize_in_progress. Then no barrier is needed for ordering of those. Would cost an extra &~1 on ->fdt fetches, though...
