From 3e469dbfe413c25d48321c3a19ddfae0727dc6e5 Mon Sep 17 00:00:00 2001 From: Andrea Arcangeli 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 Tested-By: Benoit Canet Acked-by: Paolo Bonzini Signed-off-by: Gleb Natapov --- exec.c | 1 + 1 file changed, 1 insertion(+) diff --git a/exec.c b/exec.c index 030118e68e..5e6015cbd3 100644 --- a/exec.c +++ b/exec.c @@ -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); -- GitLab