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 <[email protected]> >> --- >> 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
