Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752819AbaBCRrV (ORCPT ); Mon, 3 Feb 2014 12:47:21 -0500 Received: from mx1.redhat.com ([209.132.183.28]:58855 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751912AbaBCRrU (ORCPT ); Mon, 3 Feb 2014 12:47:20 -0500 Date: Mon, 3 Feb 2014 18:46:50 +0100 From: Oleg Nesterov To: Alex Thorlton Cc: linux-kernel@vger.kernel.org, Andrew Morton , "Kirill A. Shutemov" , Rik van Riel , Mel Gorman , Jiang Liu , Peter Zijlstra , Ingo Molnar , "Eric W. Biederman" , Robin Holt , Al Viro , Kees Cook , liguang , linux-mm@kvack.org Subject: Re: [PATCH 2/3] Add VM_INIT_DEF_MASK and PRCTL_THP_DISABLE Message-ID: <20140203174650.GA27592@redhat.com> References: <1391192628-113858-1-git-send-email-athorlton@sgi.com> <1391192628-113858-5-git-send-email-athorlton@sgi.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1391192628-113858-5-git-send-email-athorlton@sgi.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/