Messages in this thread | | | Date | Mon, 3 Feb 2014 18:46:50 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH 2/3] Add VM_INIT_DEF_MASK and PRCTL_THP_DISABLE |
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On 01/31, Alex Thorlton wrote: > > This patch adds a VM_INIT_DEF_MASK,
Perhaps it makes sense to tell a bit more... We add this mask to preserve VM_NOHUGEPAGE after fork/exec. And this is obviously affects s390, say the result of KVM_S390_ENABLE_SIE will be preserved.
I hope this is fine, but should be documented and it would be nice to have the acks from Gerald.
> --- a/kernel/sys.c > +++ b/kernel/sys.c > @@ -1996,6 +1996,23 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3, > if (arg2 || arg3 || arg4 || arg5) > return -EINVAL; > return current->no_new_privs ? 1 : 0; > + case PR_GET_THP_DISABLE: > + if (arg2 || arg3 || arg4 || arg5) > + return -EINVAL;
Cosmetic, but PR_GET_THP_DISABLE only needs to check arg2.
OTOH,
> + case PR_SET_THP_DISABLE: > + if (arg3 || arg4 || arg5) > + return -EINVAL; > + down_write(&me->mm->mmap_sem); > + if (option == PR_SET_THP_DISABLE) { > + if (arg2) > + me->mm->def_flags |= VM_NOHUGEPAGE; > + else > + me->mm->def_flags &= ~VM_NOHUGEPAGE; > + } else { > + error = !!(me->mm->def_flags & VM_NOHUGEPAGE); > + } > + up_write(&me->mm->mmap_sem); > + break;
Perhaps _GET_ doesn't even need ->mmap_sem, I do not see how the lockless "&" can get the inconsistent result. But I am fine either way.
Oleg.
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