On Mon, Jul 19, 2021 5:56 PM +0000, Peter Xu wrote: > I'm also curious what would be the real use to have an accurate PM_SWAP > accounting. To me current implementation may not provide accurate value but > should be good enough for most cases. However not sure whether it's also true > for your use case. We want the PM_SWAP bit implemented (for shared memory in the pagemap interface) to enhance the live migration for some fraction of the guest VMs that have their pages swapped out to the host swap. Once those pages are paged in and transferred over network, we then want to release them with madvise(MADV_PAGEOUT) and preserve the working set of the guest VMs to reduce the thrashing of the host swap. At this point, we don't really need the PM_UFFD_WP or PM_SOFT_DIRTY bits in the pagemap report and were considering them only if they were easy to retrieve. The latter one seems to require some plumbing through the variety of use cases in the kernel, so our intention at the moment is to capture it in the pagemap docs as the known issue, presumably to handle by CRIU users. (Cc Pavel Emelyanov CRIU chief maintainer) Thanks, Ivan
