This counter counts a specific race-condition-like fault case where a process touches a page at the exact moment the system is already writing that page back to disk. Seeing this counter increase confirms the paging subsystem is actively handling overlapping I/O and fault activity, which is normal under sustained memory pressure but worth noting if unusually frequent. For example, on a busy cluster node writing out a large batch of modified pages, a process that happens to touch one of those very pages mid-write will register here rather than in a simpler fault category.