On Mon, Jun 10, 2024 at 10:34 PM Yu Zhao <yuzhao@xxxxxxxxxx> wrote: > > On Mon, Jun 10, 2024 at 6:22 PM James Houghton <jthoughton@xxxxxxxxxx> wrote: > > > > This new notifier is for multi-gen LRU specifically > > Let me call it out before others do: we can't be this self-serving. > > > as it wants to be > > able to get and clear age information from secondary MMUs only if it can > > be done "fast". > > > > By having this notifier specifically created for MGLRU, what "fast" > > means comes down to what is "fast" enough to improve MGLRU's ability to > > reclaim most of the time. > > > > Signed-off-by: James Houghton <jthoughton@xxxxxxxxxx> > > If we'd like this to pass other MM reviewers, especially the MMU > notifier maintainers, we'd need to design a generic API that can > benefit all the *existing* users: idle page tracking [1], DAMON [2] > and MGLRU. > > Also I personally prefer to extend the existing callbacks by adding > new parameters, and on top of that, I'd try to consolidate the > existing callbacks -- it'd be less of a hard sell if my changes result > in less code, not more. > > (v2 did all these, btw.) I think consolidating the callbacks is cleanest, like you had it in v2. I really wasn't sure about this change honestly, but it was my attempt to incorporate feedback like this[3] from v4. I'll consolidate the callbacks like you had in v2. Instead of the bitmap like you had, I imagine we'll have some kind of flags argument that has bits like MMU_NOTIFIER_YOUNG_CLEAR, MMU_NOTIFIER_YOUNG_FAST_ONLY, and other ones as they come up. Does that sound ok? Do idle page tracking and DAMON need this new "fast-only" notifier? Or do they benefit from a generic API in other ways? Sorry if I missed this from some other mail. I've got feedback saying that tying the definition of "fast" to MGLRU specifically is helpful. So instead of MMU_NOTIFIER_YOUNG_FAST_ONLY, maybe MMU_NOTIFIER_YOUNG_LRU_GEN_FAST to mean "do fast-for-MGLRU notifier". It sounds like you'd prefer the more generic one. Thanks for the feedback -- I don't want to keep this series lingering on the list, so I'll try and get newer versions out sooner rather than later. [3]: https://lore.kernel.org/linux-mm/Zl5LqcusZ88QOGQY@xxxxxxxxxx/ > > [1] https://docs.kernel.org/admin-guide/mm/idle_page_tracking.html > [2] https://www.kernel.org/doc/html/latest/mm/damon/index.html
