On 1/13/20 1:03 PM, Mina Almasry wrote: > On Mon, Jan 13, 2020 at 10:44 AM Mike Kravetz <mike.kravetz@xxxxxxxxxx> wrote: >> >> On 12/17/19 3:16 PM, Mina Almasry wrote: >>> - While usage_in_bytes tracks all *faulted* hugetlb memory, >>> reservation_usage_in_bytes tracks all *reserved* hugetlb memory and >>> hugetlb memory faulted in without a prior reservation. >> >> To me, this implies that 'faults without reservations' could cause >> reservation usage to exceed reservation limit? Or, does the faulting >> process get a SIGBUS because of the reservation limit even though it >> is not using reservations? >> >> We shall see in subsequent patches. >> > > The design we went with based on previous discussions is as follows: > hugetlb pages faulted without a prior reservation get accounted at > fault time, rather than reservation time, and if the fault causes the > counter to cross the limit, the charge fails, hence the fault fails, > hence the process gets sigbus'd. Ok, sorry I did not recall the design discussion. > This means that one counter I'm adding here can cover both use cases: > if the userspace uses MAP_NORESERVE, then their memory is accounted at > fault time and they may get sigbus'd. Let's make sure this is clearly documented. Someone could be surprised if their application not using reserves gets a SIGBUS because there is a reserve limit. -- Mike Kravetz
