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 r4CasNMH 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pages mapped with incorrect > permissions, eg. COW) to the GPU requires doing either of the > following sequences: > > 1. hmm_range_fault() - fault in non-present pages with correct permissions, etc. > 2. migrate_vma_*() - migrate the pages > > Or: > > 1. migrate_vma_*() - migrate present pages > 2. If non-present pages detected by migrate_vma_*(): > a) call hmm_range_fault() to fault pages in > b) call migrate_vma_*() again to migrate now present pages > > The problem with the first sequence is that you always have to do two > page walks even when most of the time the pages are present or zero page > mappings so the common case takes a performance hit. > > The second sequence is better for the common case, but far worse if > pages aren't present because now you have to walk the page tables three > times (once to find the page is not present, once so hmm_range_fault() > can find a non-present page to fault in and once again to setup the > migration). It is also tricky to code correctly. One page table walk > could costs over 1000 cpu cycles on X86-64, which is a significant hit. > > We should be able to walk the page table once, faulting > pages in as required and replacing them with migration entries if > requested. > > Add a new flag to HMM APIs, HMM_PFN_REQ_MIGRATE, > which tells to prepare for migration also during fault handling. > Also, for the migrate_vma_setup() call paths, a flags, MIGRATE_VMA_FAULT, > is added to tell to add fault handling to migrate. > > Tested in X86-64 VM with HMM test device, passing the selftests. > Tested also rebased on the > "Remove device private pages from physical address space" series: > https://lore.kernel.org/linux-mm/20260107091823.68974-1-jniethe@nvidia.com/ > plus a small patch to adjust with no problems. > > Changes from RFC: > - rebase on 6.19-rc5 > - adjust for the device THP > - changes from feedback > > Revisions: > - RFC https://lore.kernel.org/linux-mm/20250814072045.3637192-1-mpenttil@redhat.com/ > > Cc: David Hildenbrand > Cc: Jason Gunthorpe > Cc: Leon Romanovsky > Cc: Alistair Popple > Cc: Balbir Singh > Cc: Zi Yan > Cc: Matthew Brost > Suggested-by: Alistair Popple > Signed-off-by: Mika Penttilä > > Mika Penttilä (3): > mm: unified hmm fault and migrate device pagewalk paths > mm: add new testcase for the migrate on fault case > mm:/migrate_device.c: remove migrate_vma_collect_*() functions > > include/linux/hmm.h | 17 +- > include/linux/migrate.h | 6 +- > lib/test_hmm.c | 100 +++- > lib/test_hmm_uapi.h | 19 +- > mm/hmm.c | 657 +++++++++++++++++++++++-- > mm/migrate_device.c | 589 +++------------------- > tools/testing/selftests/mm/hmm-tests.c | 54 ++ > 7 files changed, 869 insertions(+), 573 deletions(-) > I see some kernel test robot failures, I assume there will be a new version for review? Balbir