On 10/26/22 5:51 PM, Michal Hocko wrote: > On Wed 26-10-22 17:38:06, Aneesh Kumar K V wrote: >> On 10/26/22 4:32 PM, Michal Hocko wrote: >>> On Wed 26-10-22 16:12:25, Aneesh Kumar K V wrote: >>>> On 10/26/22 2:49 PM, Michal Hocko wrote: >>>>> On Wed 26-10-22 16:00:13, Feng Tang wrote: >>>>>> On Wed, Oct 26, 2022 at 03:49:48PM +0800, Aneesh Kumar K V wrote: >>>>>>> On 10/26/22 1:13 PM, Feng Tang wrote: >>>>>>>> In page reclaim path, memory could be demoted from faster memory tier >>>>>>>> to slower memory tier. Currently, there is no check about cpuset's >>>>>>>> memory policy, that even if the target demotion node is not allowd >>>>>>>> by cpuset, the demotion will still happen, which breaks the cpuset >>>>>>>> semantics. >>>>>>>> >>>>>>>> So add cpuset policy check in the demotion path and skip demotion >>>>>>>> if the demotion targets are not allowed by cpuset. >>>>>>>> >>>>>>> >>>>>>> What about the vma policy or the task memory policy? Shouldn't we respect >>>>>>> those memory policy restrictions while demoting the page? >>>>>> >>>>>> Good question! We have some basic patches to consider memory policy >>>>>> in demotion path too, which are still under test, and will be posted >>>>>> soon. And the basic idea is similar to this patch. >>>>> >>>>> For that you need to consult each vma and it's owning task(s) and that >>>>> to me sounds like something to be done in folio_check_references. >>>>> Relying on memcg to get a cpuset cgroup is really ugly and not really >>>>> 100% correct. Memory controller might be disabled and then you do not >>>>> have your association anymore. >>>>> >>>> >>>> I was looking at this recently and I am wondering whether we should worry about VM_SHARE >>>> vmas. >>>> >>>> ie, page_to_policy() can just reverse lookup just one VMA and fetch the policy right? >>> >>> How would that help for private mappings shared between parent/child? >> >> >> this is MAP_PRIVATE | MAP_SHARED? > Sorry, I meant MAP_ANONYMOUS | MAP_SHARED. > This is not a valid combination IIRC. What I meant is a simple > MAP_PRIVATE|MAP_ANON that is CoW shared between parent and child. > > [...] -aneesh
