On Tue, Sep 11, 2018 at 09:27:49AM -0600, Shuah Khan wrote: > On 09/11/2018 03:11 AM, Michal Hocko wrote: > > On Mon 10-09-18 20:02:05, Shuah Khan wrote: > >> Hi Michal, > >> > >> On 09/10/2018 07:48 AM, Michal Hocko wrote: > >>> On Fri 07-09-18 16:30:59, Shuah Khan wrote: > >>>> On 09/07/2018 02:34 AM, Michal Hocko wrote: > >>>>> On Thu 06-09-18 15:53:34, Shuah Khan wrote: > >> [....] > >>>> > >>>> In addition to isolation, being able to reserve a block instead is one > >>>> of the > >>>> issues I am looking to address. Unfortunately memory cgroups won't > >>>> address that > >>>> issue. > >>> > >>> Could you be more specific why you need reservations other than > >>> isolation. > >>> > >> > >> Taking automotive as a specific example, there are two classes of > >> applications: > >> 1. critical applications that must run > >> 2. Infotainment and misc. user-space. > >> > >> In this case, being able to reserve a block of memory for critical > >> applications > >> will ensure the memory is available for them. If a critical application > >> has to > >> restart and/or when an on-demand critical application starts, it might not > >> be able > >> to allocate memory if it is not reserved. > >> > >> When a flat system has multiple memory blocks, with NUMA emulation in > >> conjunction with > >> cpusets, one or more block can be reserved for critical applications > >> configuring a set > >> of cpus and one of more memory nodes for them. > >> > >> Memory cgroups will not support such reservation. Hope this helps explain > >> the use-case > >> I am trying to address with this patch. > > > > OK, that is more clear. I still believe that you either have to have a > > very good control over memory allocations or a good luck to not see > > unexpected kernel allocations in your reserved memory which might easily > > break guarantees you would like to accomplish. > > > > Thanks. Right. I am with you on the possibility that root cgroup can eat into > the reserved memory. However, with this solution I proposed, there is a > guarantee > that the cpuset cgroup that is configured for non-critical Infotainment and > misc. > user-space application will not be able to allocate from the reserved memory > node. > > I am hoping the proposed patch will allow critical apps. reserving memory > with the > exception that root cgroup and kernel can still allocate from it when needed. > Perhaps > cpuset exclusive logic could be extended to look for non-exclusive memory > nodes first > if it doesn't already do that. This is inline with the current cpuset > approach is that > the critical kernel allocations aren't starved to ensure memory reservations. > > If you don't think this solution isn't ideal/good, do you have other > suggestions > for solving the problem? If not would it be okay to start with what I > proposed and > build on top of as needed?
I still don't understand why this can't be achieved by faking up some NUMA entries in the firmware table and just using the existing NUMA code that we have. Will
