From 57ea2d21ae1863fd4002b2aea8ea8db8e206d464 Mon Sep 17 00:00:00 2001

From: Andrea Arcangeli <aarcange@redhat.com>

Date: Thu, 25 Jul 2013 12:11:15 +0200

Subject: [PATCH] exec: always use MADV_DONTFORK

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 <aarcange@redhat.com>

Tested-By: Benoit Canet <benoit@irqsave.net>

Acked-by: Paolo Bonzini <pbonzini@redhat.com>

Signed-off-by: Gleb Natapov <gleb@redhat.com>

(cherry picked from commit 3e469dbfe413c25d48321c3a19ddfae0727dc6e5)

Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

---

 exec.c | 1 +

 1 file changed, 1 insertion(+)

diff --git a/exec.c b/exec.c

index 394f7e2..2ea8f04 100644

--- a/exec.c

+++ b/exec.c

@@ -1172,6 +1172,7 @@ 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);