On 8/9/19 11:05 AM, Mina Almasry wrote: > On Fri, Aug 9, 2019 at 4:27 AM Michal Koutný <mkoutny@xxxxxxxx> wrote: >>> Alternatives considered: >>> [...] >> (I did not try that but) have you considered: >> 3) MAP_POPULATE while you're making the reservation, > > I have tried this, and the behaviour is not great. Basically if > userspace mmaps more memory than its cgroup limit allows with > MAP_POPULATE, the kernel will reserve the total amount requested by > the userspace, it will fault in up to the cgroup limit, and then it > will SIGBUS the task when it tries to access the rest of its > 'reserved' memory. > > So for example: > - if /proc/sys/vm/nr_hugepages == 10, and > - your cgroup limit is 5 pages, and > - you mmap(MAP_POPULATE) 7 pages. > > Then the kernel will reserve 7 pages, and will fault in 5 of those 7 > pages, and will SIGBUS you when you try to access the remaining 2 > pages. So the problem persists. Folks would still like to know they > are crossing the limits on mmap time. If you got the failure at mmap time in the MAP_POPULATE case would this be useful? Just thinking that would be a relatively simple change. -- Mike Kravetz
