On Tue, Feb 02, 2021 at 12:44:20PM -0400, Jason Gunthorpe wrote: > On Tue, Feb 02, 2021 at 11:31:27AM -0500, Peter Xu wrote: > > On Tue, Feb 02, 2021 at 04:40:33PM +0200, Gal Pressman wrote: > > > Hi Peter & Jason, > > > > Hi, Gal, Jason, > > > > > > > > It seems the hugetlb part was overlooked? > > > We're testing if the RDMA fork MADV_DONTFORK stuff can be removed on appropriate > > > kernels, but our tests still fail due to lacking explicit huge pages support [1]. > > > > I didn't think it high priority only because I think most hugetlbfs users > > should be using it shared, but maybe I'm wrong.. Then it got lost indeed. > > It turns out people are doing this: > > mmap(NULL, SEND_BUFF_SIZE, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB, -1, 0) > > Which makes some sense... Yes, thanks Jason. Though my understanding is that hugetlb pages are normally reserved in production, used with careful pre-provisioning on which app would consume how much (either 2M or 1G). Such an app (especially if it forks randomly) could actually easily exaust the huge page pool. > > Gal, you could also MADV_DONTFORK this range if you are explicitly > allocating them via special mmap. Yeah I wanted to mention this one too but I just forgot when reply: the issue thread previously pasted smells like some people would like to drop MADV_DONTFORK, but if it's able to still be applied I don't know why not.. It should still be better than depending on the coming patch imho - it marks the region as "not necessary for the fork" then we skip the whole hugetlbfs chunk. It should at least be more efficient if applicable. Thanks, -- Peter Xu
