Messages in this thread | | | Subject | Re: [PATCH 0/4] exit: Make unlikely case in mm_update_next_owner() more scalable | From | Kirill Tkhai <> | Date | Thu, 3 May 2018 13:52:51 +0300 |
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On 27.04.2018 21:05, Eric W. Biederman wrote: > Michal Hocko <mhocko@kernel.org> writes: > >> On Thu 26-04-18 21:28:18, Michal Hocko wrote: >>> On Thu 26-04-18 11:19:33, Eric W. Biederman wrote: >>>> Michal Hocko <mhocko@kernel.org> writes: >>>> >>>>> I've had a patch to remove owner few years back. It needed some work >>>>> to finish but maybe that would be a better than try to make >>>>> non-scalable thing suck less. >>>> >>>> I have a question. Would it be reasonable to just have a mm->memcg? >>>> That would appear to be the simplest solution to the problem. >>> >>> I do not remember details. Have to re-read the whole thing again. Hope >>> to get to this soon but with the current jet lag and backlog from the >>> LSFMM I rather not promis anything. Going with mm->memcg would be the >>> most simple of course but I have a very vague recollection that it was >>> not possible. Maybe I misremember... >> >> Just for the record, the last version where I've tried to remove owner >> was posted here: http://lkml.kernel.org/r/1436358472-29137-1-git-send-email-mhocko@kernel.org >> >> I didn't get to remember details yet, but the primary problem was the >> task migration between cgroups and the nasty case when different thread >> grounds share the mm. At some point I just suggested to not care >> about semantic of these weird threads all that much. We can either >> migrate all tasks sharing the mm struct or just keep the inconsistency. >> >> Anyway, removing this ugliness would be so cool! > > I suspect the only common user of CLONE_VM today is vfork. And I do > think it is crazy to migrate a process that has called vfork before > calling exec. Other useses of CLONE_VM seem even crazier. > > I think the easiest change to make in mem_cgroup_can_attach would > be just to change the test for when charges are migrated. AKA > > from: > > if (mm->owner == p) { > .... > } > > to > if (mem_cgroup_from_task(p) == mm->memcg) { > ... > } > > That allows using mm->memcg with no new limitations on when migration > can be called. In crazy cases that has the potential to change which > memcgroup the charges are accounted to, but the choice is already > somewhat arbitrary so I don't think that will be a problem. Especially > given that mm_update_next_owner does not migrate charges if the next > owner is in a different memory cgroup. A mm with tasks using it in > two different cgroups is already questionable if not outright > problematic. > > > Kirill Tkhai do you think you would be able adapt Michal Hoko's old > patch at https://marc.info/?l=linux-kernel&m=143635857131756&w=2 > that replaces mm->owner with mm->memcg?
I was at vacation. Sorry for the late reply.
> We probably want to outlaw migrating an mm where we are not migrating > all of the mm->users eventually. Just because that case is crazy. > But it doesn't look like we need to do that to fix the memory control > group data structures.
Kirill
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