On Wed, Feb 22, 2023 at 3:56 PM Yu Zhao <yuzhao@xxxxxxxxxx> wrote: > > Currently anonymous folios only support two orders: 0 and the PMD > order. Flexible orders for anonymous folios can resist both internal > or external fragmentations when the PMD order is too underutilized or > costly to allocate. Flexible orders can also leverage the TLB > coalescing feature, .e.g., order 3 for AMD and order 4 for ARM CPUs. > > Discussion points: > 1. The page fault path: determining the best order and the fallback policy. > 2. The reclaim path: detecting the utilization and the splitting policy. > 3. The refcount and the mapcount models, e.g., reuse the PMD-mapped > THP model or not. > 4. The splitting, and the collapsing if needed. > 5. Other paths: COW, GUP, madvise(), mprotect(), page migration, etc. > > A bit of history: > I discussed this topic at Matthew's THP Cabal meeting a couple of > years ago, as one of the major use cases of folios. Around the same > time, I tried to get Hugh to work with me on it, since he tried > something similar back in 2001 [1]. William's page clustering from > 2003 [2] is also based on that, btw. Then I put the idea on the back > burner. > > Now it seems to be a good time to revisit. Yang Shi and I have been > looking at some details, trying to scope out the work that would be > required. We don't have anything definitive yet, but we should have > enough to share by the time of the LSF/MM/BPF. This might be useful for Android. I would like to participate in this discussion. > > [1] https://lore.kernel.org/linux-mm/Pine.LNX.4.21.0107051737340.1577-100000@localhost.localdomain/ > [2] https://lwn.net/Articles/23785/ >
