From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:51698) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1V6kY1-0001d6-DV for qemu-devel@nongnu.org; Tue, 06 Aug 2013 12:55:56 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1V6kXi-0006mI-SH for qemu-devel@nongnu.org; Tue, 06 Aug 2013 12:55:49 -0400 Message-ID: <52012A7E.90800@suse.de> Date: Tue, 06 Aug 2013 18:55:26 +0200 From: =?ISO-8859-1?Q?Andreas_F=E4rber?= MIME-Version: 1.0 References: <1374747075-7172-1-git-send-email-aarcange@redhat.com> <20130725103220.GH10517@redhat.com> In-Reply-To: <20130725103220.GH10517@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH] KVM: always use MADV_DONTFORK List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Andrea Arcangeli , Paolo Bonzini Cc: Peter Maydell , qemu-devel@nongnu.org, Gleb Natapov , qemu-stable@nongnu.org Am 25.07.2013 12:32, schrieb Andrea Arcangeli: > On Thu, Jul 25, 2013 at 11:16:44AM +0100, Peter Maydell wrote: >> On 25 July 2013 11:11, Andrea Arcangeli wrote: >>> diff --git a/exec.c b/exec.c >>> index c99a883..d3bb58d 100644 >>> --- a/exec.c >>> +++ b/exec.c >>> @@ -1162,6 +1162,7 @@ ram_addr_t qemu_ram_alloc_from_ptr(ram_addr_t s= ize, void *host, >>> >>> qemu_ram_setup_dump(new_block->host, size); >>> qemu_madvise(new_block->host, size, QEMU_MADV_HUGEPAGE); >>> + qemu_madvise(new_block->host, size, QEMU_MADV_DONTFORK); >>> >>> if (kvm_enabled()) >>> kvm_setup_guest_memory(new_block->host, size); >>> >> >> kvm_setup_guest_memory() already calls >> qemu_madvise(start, size, QEMU_MADV_DONTFORK) >> so why do we need to do it here as well? >=20 > That only runs if kvm is enabled and mmu is not sync. But we need it > in the common case too, to prevent -ENOMEM (if MADV_DONTFORK is > available in the host OS, otherwise well we'll just do best effort and > skip). See commit message for more details. So if we add the DONTFORK unconditionally here, why not drop it in said kvm_setup_guest_memory()? That would make the patch more self-documenting while at it. Andreas >=20 >> If we should be doing it in all cases presumably the right >> fix is to move the if (!kvm_has_sync_mmu()) check in >> kvm_setup_guest_memory() from "do we call madvise" to >> "do we fail with an error if it failed". >=20 > We could pass an error to kvm_setup_guest_memory but it's not worth it > considering more likely we should abort if kvm is enabled and mmu is > not sync (without bothering to call MADV_DONTFORK there). >=20 --=20 SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 N=FCrnberg, Germany GF: Jeff Hawn, Jennifer Guild, Felix Imend=F6rffer; HRB 16746 AG N=FCrnbe= rg