> -----Original Message----- > From: Gonzalez Monroy, Sergio > Sent: Tuesday, July 11, 2017 7:36 PM > To: Tan, Jianfeng; Stephen Hemminger; dev@dpdk.org > Subject: Re: [dpdk-dev] [RFC] pci: force address of mappings in secondary > process > > On 11/07/2017 02:56, Tan, Jianfeng wrote: > >> -----Original Message----- > >> From: dev [mailto:dev-boun...@dpdk.org] On Behalf Of Stephen > >> Hemminger > >> Sent: Tuesday, July 11, 2017 9:13 AM > >> To: dev@dpdk.org > >> Cc: Stephen Hemminger > >> Subject: [dpdk-dev] [RFC] pci: force address of mappings in secondary > >> process > >> > >> The PCI memory resources in the secondary process should be in > >> the exact same location as the primary process. Otherwise > >> there is a risk of a stray pointer. > >> > >> Not sure if this is right, but it looks like a potential > >> problem. > >> > >> --- > >> lib/librte_eal/common/eal_common_pci_uio.c | 2 +- > >> 1 file changed, 1 insertion(+), 1 deletion(-) > >> > >> diff --git a/lib/librte_eal/common/eal_common_pci_uio.c > >> b/lib/librte_eal/common/eal_common_pci_uio.c > >> index 367a6816dcb8..2156b1a436c4 100644 > >> --- a/lib/librte_eal/common/eal_common_pci_uio.c > >> +++ b/lib/librte_eal/common/eal_common_pci_uio.c > >> @@ -77,7 +77,7 @@ pci_uio_map_secondary(struct rte_pci_device *dev) > >> > >> void *mapaddr = pci_map_resource(uio_res- > >>> maps[i].addr, > >> fd, (off_t)uio_res->maps[i].offset, > >> - (size_t)uio_res->maps[i].size, 0); > >> + (size_t)uio_res->maps[i].size, > >> MAP_FIXED); > >> /* fd is not needed in slave process, close it */ > >> close(fd); > >> if (mapaddr != uio_res->maps[i].addr) { > >> -- > >> 2.11.0 > > +1 for this RFC. I also once encounter such problem, and I use the same > way to solve it. The addr parameter of mmap() syscall is only a hint instead > of > a must even the VMA is not occupied yet. > > > > Thanks, > > Jianfeng > > How do you know the VMA is not occupied?
I did by check /proc/self/maps. > > I think the risk here is that the dynamic linker loaded some shared > library in that VMA, and forcing MAP_FIXED is not a safe solution. > What I have observed is that Linux will return a different VMA than the > one hinted when there is already a mapping in the requested/hinted VMA. IMO, that's not the target of this RFC. The target is to solve the situation (in current primary/secondary model) that kernel will not use the addr even there's no VMA on that addr. This is my understanding, Stephen, please correct me if I'm wrong. > > I reckon this is a similar issue as we have with the multi-process model > when we do not get the VMA requested for the huge-pages. > AFAIK we do not have a robust solution for this issue other than restart > the program and hope the dynamic linker does not map anything in the VMA > ranges that we need to map from the primary. This is also assuming that > the application does not allocate memory and maps things before calling > eal_init as it could potentially use VMA ranges that we need in the > secondary process. This is another problem. > > The proposal for new secondary process model would solve these issues: > http://dpdk.org/ml/archives/dev/2017-May/066147.html And yes, this might happen to solve the targeted issue in this RFC. But before the new model is out, this patch seems a workable way for the original issue. Thanks, Jianfeng > > Thanks, > Sergio
