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From: "Benoît Canet" <benoit.canet@irqsave.net>
To: Andrea Arcangeli <aarcange@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	qemu-devel@nongnu.org, Gleb Natapov <gleb@redhat.com>,
	qemu-stable@nongnu.org
Subject: Re: [Qemu-devel] [PATCH] KVM: always use MADV_DONTFORK
Date: Tue, 6 Aug 2013 19:06:20 +0200	[thread overview]
Message-ID: <20130806170619.GD5068@irqsave.net> (raw)
In-Reply-To: <1374747075-7172-1-git-send-email-aarcange@redhat.com>

Le Thursday 25 Jul 2013 à 12:11:15 (+0200), Andrea Arcangeli a écrit :
> 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>
> ---
>  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);
> 

This patch solve a bug where the network down script of a regular tap interface
is not executed because fork fail when a pci-assigment is done on a large guest.

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

  parent reply	other threads:[~2013-08-06 17:04 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-07-25 10:11 [Qemu-devel] [PATCH] KVM: always use MADV_DONTFORK Andrea Arcangeli
2013-07-25 10:16 ` Peter Maydell
2013-07-25 10:32   ` Andrea Arcangeli
2013-08-06 16:55     ` Andreas Färber
2013-08-30 15:48       ` Paolo Bonzini
2013-08-06 16:47 ` [Qemu-devel] PING for-1.6 " Paolo Bonzini
2013-08-30 15:48   ` [Qemu-devel] PING^2 " Paolo Bonzini
2013-08-30 15:52     ` Andreas Färber
2013-08-30 16:03       ` Paolo Bonzini
2013-08-30 16:21         ` Gleb Natapov
2013-08-30 16:40           ` Paolo Bonzini
2013-08-06 17:06 ` Benoît Canet [this message]
2013-09-01  9:39 ` [Qemu-devel] " Gleb Natapov

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