From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx137.postini.com [74.125.245.137]) by kanga.kvack.org (Postfix) with SMTP id E0DD86B0005 for ; Wed, 6 Feb 2013 15:51:05 -0500 (EST) Date: Wed, 6 Feb 2013 12:51:03 -0800 From: Andrew Morton Subject: Re: [PATCH] mm: don't overwrite mm->def_flags in do_mlockall() Message-Id: <20130206125103.61748ed0.akpm@linux-foundation.org> In-Reply-To: <1360165774-55458-1-git-send-email-gerald.schaefer@de.ibm.com> References: <1360165774-55458-1-git-send-email-gerald.schaefer@de.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Gerald Schaefer Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Vivek Goyal , Hugh Dickins , David Rientjes , Mel Gorman , Martin Schwidefsky , Heiko Carstens , Michel Lespinasse On Wed, 6 Feb 2013 16:49:34 +0100 Gerald Schaefer wrote: > With commit 8e72033 "thp: make MADV_HUGEPAGE check for mm->def_flags" > the VM_NOHUGEPAGE flag may be set on s390 in mm->def_flags for certain > processes, to prevent future thp mappings. This would be overwritten > by do_mlockall(), which sets it back to 0 with an optional VM_LOCKED > flag set. > > To fix this, instead of overwriting mm->def_flags in do_mlockall(), > only the VM_LOCKED flag should be set or cleared. What are the user-visible effects here? Looking at the 274023da1e8 changelog, I'm guessing that it might be pretty nasty - kvm breakage? > --- a/mm/mlock.c > +++ b/mm/mlock.c > @@ -517,11 +517,11 @@ SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len) > static int do_mlockall(int flags) > { > struct vm_area_struct * vma, * prev = NULL; > - unsigned int def_flags = 0; > > if (flags & MCL_FUTURE) > - def_flags = VM_LOCKED; > - current->mm->def_flags = def_flags; > + current->mm->def_flags |= VM_LOCKED; > + else > + current->mm->def_flags &= ~VM_LOCKED; > if (flags == MCL_FUTURE) > goto out; Michal sent an equivalent patch last month: http://ozlabs.org/~akpm/mmotm/broken-out/mm-make-mlockall-preserve-flags-other-than-vm_locked-in-def_flags.patch. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org