From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:42675) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VFQw4-0001X1-Tx for qemu-devel@nongnu.org; Fri, 30 Aug 2013 11:48:41 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1VFQvw-0007RI-GR for qemu-devel@nongnu.org; Fri, 30 Aug 2013 11:48:32 -0400 Sender: Paolo Bonzini Message-ID: <5220BEC1.5040908@redhat.com> Date: Fri, 30 Aug 2013 17:48:17 +0200 From: Paolo Bonzini MIME-Version: 1.0 References: <1374747075-7172-1-git-send-email-aarcange@redhat.com> <5201289C.4040809@redhat.com> In-Reply-To: <5201289C.4040809@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: [Qemu-devel] PING^2 Re: [PATCH] KVM: always use MADV_DONTFORK List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Andrea Arcangeli , qemu-devel@nongnu.org, Gleb Natapov , qemu-stable@nongnu.org Il 06/08/2013 18:47, Paolo Bonzini ha scritto: > 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 > > PING^2 The last paragraph of the commit message should answer Andreas's objection. Paolo