On 2016/7/21 21:40, Michal Hocko wrote: > On Thu 21-07-16 21:25:38, zhong jiang wrote: >> On 2016/7/21 20:55, Michal Hocko wrote: > [...] >>> OK, now I understand what you mean. So you mean that a different process >>> initiates the migration while this path copies to pte. That is certainly >>> possible but I still fail to see what is the problem about that. >>> huge_pte_alloc will return the identical pte whether it is regular or >>> migration one. So what exactly is the problem? >>> >> copy_hugetlb_page_range obtain the shared dst_pte, it may be not equal >> to the src_pte. The dst_pte can come from other process sharing the >> mapping. > So you mean that the parent doesn't have the shared pte while the child > would get one? > no, parent must have the shared pte because the the child copy the parent. but parent is not the only source pte we can get. when we scan the maping->i_mmap, firstly ,it can obtain a shared pte from other process. but I am not sure. >> /* If the pagetables are shared don't copy or take references */ >> if (dst_pte == src_pte) >> continue; >> >> Even it do the fork path, we scan the i_mmap to find same pte. I think >> that dst_pte may come from other process. It is not the parent. it >> will lead to the dst_pte is not equal to the src_pte from the parent. > Let's say this would be possible (I am not really sure but for the sake > of argumentation), if the src is not shared while dst is shared and the > page is under migration then all the page table should be marked as > swap migrate entries no? If they are not and copy_hugetlb_page_range > cannot handle with that then it is a bug in copy_hugetlb_page_range > which doesn't have anything to do with the BUG_ON in huge_pte_alloc. > So I would argue that if the problem exists at all it is a separate > issue IMHO. yes, it is a separate issule. > Naoya, could you comment on that please? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>