On Sat, Apr 25, 2026 at 08:05:16AM +0200, David Hildenbrand (Arm) wrote: > On 4/24/26 15:49, Kiryl Shutsemau wrote: > > On Fri, Apr 24, 2026 at 07:51:44AM -0400, Peter Xu wrote: > >> On Fri, Apr 24, 2026 at 11:34:48AM +0100, Kiryl Shutsemau wrote: > >>> Both page_idle and the LRUs (legacy or MGLRU) track accesses on physical > >>> memory. We need visibility in the virtual address space domain. > >> > >> Yes they are, but ACCESS bit isn't. > > > > A-bit is not a reliable signal for userspace working-set tracking > > because the kernel itself is a concurrent consumer. > Right, I don't think we want to rely on either the A bit just like we don't > want > to rely on the Dirty bit in other code. (and even SoftDirty bit is a flawed > concept) > > I do see some value in a reliable RWP mechanism based on uffd. The real > question > is, how much benefit it would bring (which other use cases could benefit from > it).
I have not put much thought into use-cases beyond VMs, but I think other mmap-heavy loads (databases, GC'd runtimes, etc) can make a use in a similar way: workset tracking and organizing userspace-driven memory tiering based on the workset data. -- Kiryl Shutsemau / Kirill A. Shutemov
