Hi Aneesh, On Sun, 19 Feb 2023 19:59:47 +0530 "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxx> wrote: > SeongJae Park <sj@xxxxxxxxxx> writes: > > > Hi Aneesh, > > > > On Fri, 17 Feb 2023 17:28:09 +0530 Aneesh Kumar K V <aneesh.kumar@xxxxxxxxxxxxx> wrote: > > > >> PowerPC architecture (POWER10) supports a Hot/Cold page tracking > >> facility that provides access counter and access affinity details at > >> configurable page size granularity [1]. I have been looking at using > >> this counter in different areas of the kernel such as > >> > >> 1) Page reclaim/demotion > >> 2) THP utilization > >> 3) Page promotion. > >> > >> I have done some MGLRU integration and would like to discuss the > >> observation with the rest of the community. It is still not clear what > >> are the best ways to integrate these hardware counters in the Linux > >> kernel. > > > > Sounds very interesting. I think DAMON might be one another option, because it > > is designed to be easy to extended with various source of access > > information[1], and provides an abstraction layer for access temparature based > > memory management[2], namely Data Access Monitoring-based Operation Schemes > > (DAMOS). > > > >> Attached is the performance graph showing how the mongodb/ycsb > >> benchmark performs when using hardware counters with MGLRU aging. An > >> early RFC version of the code can be found at > >> https://github.com/kvaneesh/linux/commit/b472e2c8080823bb4114c286270aea3e18ffe221 > >> . I also expect we can get some numbers w.r.t THP usage before the > >> conference. > > > > I also have experimented a DAMON-based THP optimization[3], which shown > > interesting results. > > > > Hope to discuss about this with you at LSF/MM. FYI, I also proposed an LSF/MM > > topic for DAMON[4]. > > > > [1] https://docs.kernel.org/mm/damon/design.html#configurable-layers > > [2] https://docs.kernel.org/mm/damon/api.html#c.damos > > [3] https://www.amazon.science/publications/daos-data-access-aware-operating-system > > [4] https://lore.kernel.org/damon/20230214003328.55285-1-sj@xxxxxxxxxx/ > > > > > > The hardware counters that are supported in the case of POWER10 are > based on physical addresses. The hardware facility will count the access > across a physical address range and there is a counter for each page > that gives the access count and also information about which node did > access the page. > > I haven't spent much time studying DAMON so I might be wrong here. The > reason I avoided using DAMON for the POC was because my goal was to > evaluate how the hardware counters measured against the pte reference > bit and I was not sure I could evaluate that using the DAMON action > facility. > > I do agree that we could add a layer similar to DAMON_PADDR and expose > the details to userspace. But I was not sure we can take action based on > that. In most cases what I wanted was to move the coldest page in the > Numa node to swap. So that is relative hotness rather than moving a page > that got a hotness value less than 10 to swap even though we can figure > out a way to make the latter similar to the former. I think you could use DAMOS quota[1]. Under the quota, DAMOS prioritizes regions based on the access pattern, and applies the action to higher-priority regions, so you can do relative coldness-based reclamation, like DAMON_RECLAIM does[2]. The interface might not very efficient for your specific case, though. I want to know such cases and improve the interface or implement new features. [1] https://docs.kernel.org/mm/damon/api.html#c.damos_quota [2] https://docs.kernel.org/admin-guide/mm/damon/reclaim.html#quota-sz > > > I will look at DAMON and see if that is the best framework for things > like this. Great, please feel free to reach out to me if you have any question or need help. Thanks, SJ > > -aneesh
