Hi, Alistair, On Fri, Aug 12, 2022 at 03:22:30PM +1000, Alistair Popple wrote: > migrate_vma_setup() has a fast path in migrate_vma_collect_pmd() that > installs migration entries directly if it can lock the migrating page. > When removing a dirty pte the dirty bit is supposed to be carried over > to the underlying page to prevent it being lost. > > Currently migrate_vma_*() can only be used for private anonymous > mappings. That means loss of the dirty bit usually doesn't result in > data loss because these pages are typically not file-backed. However > pages may be backed by swap storage which can result in data loss if an > attempt is made to migrate a dirty page that doesn't yet have the > PageDirty flag set. > > In this case migration will fail due to unexpected references but the > dirty pte bit will be lost. If the page is subsequently reclaimed data > won't be written back to swap storage as it is considered uptodate, > resulting in data loss if the page is subsequently accessed. > > Prevent this by copying the dirty bit to the page when removing the pte > to match what try_to_migrate_one() does. > > Signed-off-by: Alistair Popple <apopple@xxxxxxxxxx> > Reported-by: Peter Xu <peterx@xxxxxxxxxx> This line should be: Reported-by: Huang Ying <ying.huang@xxxxxxxxx> Please also feel free to add: Acked-by: Peter Xu <peterx@xxxxxxxxxx> Thanks, -- Peter Xu
