On Wed, Mar 27, 2024 at 03:53:39PM -0700, Yuanchu Xie wrote: > On Wed, Mar 27, 2024 at 2:44 PM Gregory Price > <gregory.price@xxxxxxxxxxxx> wrote: > > > > Please note that this proposed interface (move_phys_pages) is very > > unlikely to be received upstream due to side channel concerns. Instead, > > it's more likely that the tiering component will expose a "promote X > > pages from tier A to tier B", and the kernel component would then > > use/consume hotness information to determine which pages to promote. > > I see that mm/memory-tiers.c only has support for demotion. What kind > of hotness information do devices typically provide? The OCP proposal > is not very specific about this. > A list of hot pages with configurable threshold? > Access frequency for all pages at configured granularity? > Is there a way to tell which NUMA node is accessing them, for page promotion? (caveat: i'm not a memory-tiers maintainer, you may want to poke at them directly for more information, this is simply spitballing an idea) I don't know of any public proposals of explicit hotness information provided by hardware yet, just the general proposal. For the sake of simplicity, I would make the assumption that you have the least information possible - a simple list of "hot addresses" in Host Physcal Address format. I.e. there's some driver function that amounts to: uint32_t device_get_hot_addresses(uint64_t *addresses, uint32_t buf_max); Where the return value is number of addresses the device returned, and the buf_max is the number of addresses that can be read. Drives providing this functionality would then register this as a callback when its memory becomes a member of some numa node. Re: source node - Devices have no real way of determining upstream source information. > > > > (Just as one example, there are many more realistic designs) > > > > So if there is a way to expose workingset data to the mm/memory_tiers.c > > component instead of via sysfs/cgroup - that is preferable. > > Appreciate the feedback. The data in its current form might be useful > to inform demotion decisions, but for promotion, are you aware of any > recent developments? I would like to encode hotness as workingset data > as well. There were some recent patches to DAMON about promotion/demotion. You might look there. ~Gregory
