On 09/11/2018 10:50 AM, Will Deacon wrote: > 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. >
That is what is this patch is doing in some ways. Instead of hacking the firmware tables, it provides a command line option to split the flat machine into specified number of NUMA memory nodes. In addition to the new config option and new command line handling, I added one init routine that handles the NUMA emulation and after that normal NUMA code is leveraged. The only change is the following added to arm64_numa_init() if (!numa_init(arm64_numa_emu_init)) + return; arm64_numa_emu_init() does nothing unless the kernel is booted with the new "numa=fake=N" Please note that I am not adding any new NUMA code other than just this init routine. When the command line is specified, instead of going down the dummy_numa_init() path it will create NUMA emulation nodes. I was very careful in identifying the minimal amount of code needed to add this support. The change is limited to two existing routines: numa_parse_early_param() and arm64_numa_init(). numa_init() which is common for all the variants including the fallback dummy_numa_init() This allows a cleaner way to split the memory and leverage all of the NUMA code. This makes it easier to debug problems as opposed to hacked firmware tables. thanks, -- Shuah
