Am 30.08.2013 17:48, schrieb Paolo Bonzini: > 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.
OK. The patch is mislabelled as "KVM:" though putting this in a common code path and touching exec.c only, so please put it on uq/master and fix that up before you set the history in stone. :) Andreas -- SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer; HRB 16746 AG Nürnberg
