From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49704) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1V6kQ7-00037C-FK for qemu-devel@nongnu.org; Tue, 06 Aug 2013 12:47:48 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1V6kPz-0002wZ-1T for qemu-devel@nongnu.org; Tue, 06 Aug 2013 12:47:39 -0400 Sender: Paolo Bonzini Message-ID: <5201289C.4040809@redhat.com> Date: Tue, 06 Aug 2013 18:47:24 +0200 From: Paolo Bonzini MIME-Version: 1.0 References: <1374747075-7172-1-git-send-email-aarcange@redhat.com> In-Reply-To: <1374747075-7172-1-git-send-email-aarcange@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: [Qemu-devel] PING for-1.6 Re: [PATCH] KVM: always use MADV_DONTFORK List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Andrea Arcangeli Cc: qemu-devel@nongnu.org, Gleb Natapov , qemu-stable@nongnu.org On 07/25/2013 12:11 PM, Andrea Arcangeli wrote: > MADV_DONTFORK prevents fork to fail with -ENOMEM if the default > overcommit heuristics decides there's too much anonymous virtual > memory allocated. If the KVM secondary MMU is synchronized with MMU > notifiers or not, doesn't make a difference in that regard. > > Secondly it's always more efficient to avoid copying the guest > physical address space in the fork child (so we avoid to mark all the > guest memory readonly in the parent and so we skip the establishment > and teardown of lots of pagetables in the child). > > In the common case we can ignore the error if MADV_DONTFORK is not > available. Leave a second invocation that errors out in the KVM path > if MMU notifiers are missing and KVM is enabled, to abort in such > case. > > Signed-off-by: Andrea Arcangeli > --- > exec.c | 1 + > 1 file changed, 1 insertion(+) > > 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 size, 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); > > PING. Benoit reported this on IRC, too. Paolo