On Thu, Apr 23, 2026 at 10:50:06AM -0400, Peter Xu wrote: > Hello, Kiryl, > > On Thu, Apr 23, 2026 at 03:27:11PM +0100, Kiryl Shutsemau wrote: > > The patchet is pretty good shape in my eyes and will probably drop RFC > > tag. > > I still have some high level questions not yet got answered. Do you want > to answer them? > > https://lore.kernel.org/all/[email protected]/
Sorry, reply to this got lost in my TODO list. > In summary, it's about: > > - Whether we have explored other approaches on page hotness tracking So, for read/write tracking we have clear_refs=1, page_idle and DAMON. Did I miss something? clear_refs is process-wide hammer. And you can miss a hot page if it races with LRU rotation. page_idle needs rmap. It will not scale. DAMON is built around sampling. It is good for working set estimation, but I don't think it is directly useful for eviction decision. It can miss hot pages. LRU rotation will also loose info. None of them gives comparable capabilities. We also need a mechanism to atomically evict pages. > - Whether read protection is required for an userspace swap system > (e.g. did you get time to have a look at umap?) I looked at it briefly, so I can miss details. IIUC, in absence of read tracking it doesn't collect hotness information at all. The eviction is based on fault-in time: the oldest faulted-in page gets evicted first. I guess it is fine if you don't care much about refault cost. Like, if your workload fits into memory completely and refaults are rare. That's not my case. -- Kiryl Shutsemau / Kirill A. Shutemov
