Finally I start to post formal patches because it's growing. And also since we've discussed quite some issues already, so I feel like it's clearer on what we need to do, and how. This series is majorly inspired by the previous discussion on the list [1], starting from the report from Jason on the rdma test failure. Linus proposed the solution, which seems to be a very nice approach to avoid the breakage of userspace apps that didn't use MADV_DONTFORK properly before. More information can be found in that thread too. I believe the initial plan was to consider merging something like this for rc7/rc8. However now I'm not sure due to the fact that the code change in copy_pte_range() is probably more than expected, so it can be with some risk. I'll leave this question to the reviewers... I tested it myself with fork() after vfio pinning a bunch of device pages, and I verified that the new copy pte logic worked as expected at least in the most general path. However I didn't test thp case yet because afaict vfio does not support thp backed dma pages. Luckily, the pmd/pud thp patch is much more straightforward than the pte one, so hopefully it can be directly verified by some code review plus some more heavy-weight rdma tests. Patch 1: Introduce mm.has_pinned (as single patch as suggested by Jason) Patch 2-3: Some slight rework on copy_page_range() path as preparation Patch 4: Early cow solution for pte copy for pinned pages Patch 5: Same as above, but for thp (pmd/pud). Hugetlbfs fix is still missing, but as planned, that's not urgent so we can work upon. Comments greatly welcomed. Thanks. Peter Xu (5): mm: Introduce mm_struct.has_pinned mm/fork: Pass new vma pointer into copy_page_range() mm: Rework return value for copy_one_pte() mm: Do early cow for pinned pages during fork() for ptes mm/thp: Split huge pmds/puds if they're pinned when fork() include/linux/mm.h | 2 +- include/linux/mm_types.h | 10 ++ kernel/fork.c | 3 +- mm/gup.c | 6 ++ mm/huge_memory.c | 26 +++++ mm/memory.c | 226 +++++++++++++++++++++++++++++++++++---- 6 files changed, 248 insertions(+), 25 deletions(-) -- 2.26.2
