Hi Everyone, I have noticed a change in the synchrony of updating the soft-dirty bits in recent kernel versions (5.6+). More precisely, up to kernel v5.5, the soft-dirty bits as parsed from /proc/pid/pagemap accurately capture the dirtied pages. Recently, I started testing on kernels v5.6 - v5.9, and I noticed that the soft-dirty bits are not immediately updated. I have prepared a short test that repeatedly causes at least one memory page to be dirtied, then scans /proc/pid/pagemap counting the soft-dirty bits. The test fails if this count is zero. In my observation, this test fails once in every 10-20 trials. The test defaults to 100 trials and can be found at https://gitlab.mpi-sws.org/-/snippets/1696 Is this non-synchronous propagation of soft dirty bits intended? If yes, is there a way to force the soft-dirty bits to be propagated to the page map entries immediately, or is there an alternative interface that has the synchronous behavior? Thanks in advance, Mohamed Alzayat
