On Wed, Aug 18, 2021 at 11:07 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > On Wed, Aug 18, 2021 at 10:02:46PM +0800, Muchun Song wrote: > > On Tue, Aug 17, 2021 at 9:43 AM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > > > > + unsigned int target, nnodes; > > > > > int i; > > > > > int nid; > > > > > + /* > > > > > + * The barrier will stabilize the nodemask in a register or on > > > > > + * the stack so that it will stop changing under the code. > > > > > + * > > > > > + * Between first_node() and next_node(), pol->nodes could be changed > > > > > + * by other threads. So we put pol->nodes in a local stack. > > > > > + */ > > > > > + barrier(); > > > > > > I think this could be an smp_rmb()? > > > > Hi Matthew, > > > > I have a question. Why is barrier() not enough? > > I think barrier() may be more than is necessary. We don't need a > barrier on non-SMP systems (or do we?) And we only need to order reads, > not writes. Here barrier() is just a compiler barrier, which is cheaper than smp_rmb() which usually equals to memory barrier instruction plus barrier(). So I think barrier() , which will stabilize the nodemask in a register or on the stack, is more appropriate here. Thanks.
