damage tracking
also: dirty page tracking, dirty tracking, page tracking
A kernel mechanism that records which memory pages have been modified since the last checkpoint, enabling efficient backups and live migration by only copying changed data.
Damage tracking (also called dirty page tracking) is a kernel feature that monitors write operations to memory and maintains a record of which pages have been altered. This allows systems to identify only the changed portions of memory rather than copying everything.
The primary use cases are live VM migration—where a running virtual machine is moved between physical hosts—and incremental backups. During live migration, the kernel marks pages as "dirty" when they're written to, so only dirty pages need to be retransmitted if the source VM continues running during the migration process.
For example, a backup utility can use damage tracking to perform an initial full backup of a filesystem, then on subsequent runs, only backup pages that have been modified since the last backup. This significantly reduces backup time and storage requirements.
Damage tracking is typically implemented using write-protection mechanisms at the page table level or through dedicated kernel data structures that flag modified pages.