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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>
This commit is contained in:
Andrea Arcangeli 2013-07-25 12:11:15 +02:00 committed by Paolo Bonzini
parent 2d1fe1873a
commit 3e469dbfe4
1 changed files with 1 additions and 0 deletions
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exec.c
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@ -1157,6 +1157,7 @@ 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);