Hi all, Not too long ago I took some time to investigate the possibility of scanning physical memory directly by traversing the memory map directly rather than the LRU linked list. This was inspired by a post from Matthew [0] wherein he demonstrated just how significant the difference is between traversing arrays of contiguous data on a modern system vs. the almost worst-case scenario of traversing a linked-list. I tested how this might look by implementing code which simply traverses and filters the memory map for LRU pages, simplifying as much as possible. However no matter which machine (ranging from 16 GB - 192 GB) or whether virtualised or real hardware, I found unfortunately disappointing results - the act of having to scan such a large range of memory resulted in performance significantly less than a typical LRU scan at low memory utilisation and performance at best matching LRU scanning at high memory utilisation (simulating higher memory pressure). There are a number of factors at play here, and perhaps the shrinkage of struct page (allowing for denser placement in cache lines), or an improved algorithm might lead to more promising results. Having discussed this with Matthew, he suggested I put forward a proposal to discuss this area in order that we can learn from this should it appear this approach is unworkable or perhaps determine whether there might be something to this that we might still salvage. I intend to do some more research and generate some more specific numbers (feel free to give feedback here) before LSF so we can have something more specific to talk about. I always envisioned this approach being somehow integrated with MGLRU and I wonder if some hybrid means of integrating this approach with the MGLRU one might make sense, which could also be another area of discussion. Thanks! [0]:https://lore.kernel.org/linux-mm/ZTc7SHQ4RbPkD3eZ@xxxxxxxxxxxxxxxxxxxx/
