From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:52893) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1V2IW4-00068B-3f for qemu-devel@nongnu.org; Thu, 25 Jul 2013 06:11:27 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1V2IW1-0001b0-6N for qemu-devel@nongnu.org; Thu, 25 Jul 2013 06:11:24 -0400 From: Andrea Arcangeli Date: Thu, 25 Jul 2013 12:11:15 +0200 Message-Id: <1374747075-7172-1-git-send-email-aarcange@redhat.com> Subject: [Qemu-devel] [PATCH] KVM: always use MADV_DONTFORK List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org, qemu-stable@nongnu.org Cc: Paolo Bonzini , Gleb Natapov 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);