On Wed, Mar 27, 2024 at 2:44 PM Gregory Price <gregory.price@xxxxxxxxxxxx> wrote: > > On Wed, Mar 27, 2024 at 02:30:59PM -0700, Yuanchu Xie wrote: > > I realize this does not generalize well to hotness information, but I > > lack the intuition for an abstraction that presents hotness in a useful > > way. Based on a recent proposal for move_phys_pages[2], it seems like > > userspace tiering software would like to move specific physical pages, > > instead of informing the kernel "move x number of hot pages to y > > device". Please advise. > > > > [2] > > https://lore.kernel.org/lkml/20240319172609.332900-1-gregory.price@xxxxxxxxxxxx/ > > > > 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? > > (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. > > The 'move_phys_pages' interface is more of an experimental interface to > test the effectiveness of this approach without having to plumb out the > entire system. Definitely anything userland interface should not be > designed to generate physical address information for consumption unless > it is hard-locked behind admin caps. > > Regards, > Gregory
