From: Dan Williams <dan.j.williams@intel.com>
To: Yigal Korman <yigal@plexistor.com>
Cc: "linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>
Subject: Re: qemu-kvm hangs with DAX
Date: Thu, 20 Apr 2017 06:23:18 -0700 [thread overview]
Message-ID: <CAPcyv4hi2DicbTR3-m735jhP=mdMU+QMZY-9FP+eXU7VFuV79A@mail.gmail.com> (raw)
In-Reply-To: <CACTTzNaOc2K5tgfbp-zfr=C9Xd2s1g-9y6rXiNbjPH9iK-HsWw@mail.gmail.com>
On Thu, Apr 20, 2017 at 2:19 AM, Yigal Korman <yigal@plexistor.com> wrote:
> Hi everyone,
>
> I have an interesting issue with DAX and KVM - I'm trying to boot a VM
> with its memory mapped to a DAX-mounted file (kernel 4.9).
>
> The use case is a bit wacky but I'm trying to recreate something
> similar to what clearlinux[1] described (although they don't use this
> method anymore).
>
> When mapping the memory to a regular ext4 file, the VM boots fine.
> But when mapping to ext4+dax, the VM won't boot or perhaps boots
> extremely slowly.
> In both cases the FS is on a memory pmem device.
>
> Here's a snippet of how I load things:
>
> mkfs.ext4 /dev/pmem0
> mount /dev/pmem0 /mnt
> fallocate -l 512M /mnt/mem
I wonder if you replace this with "dd if=/dev/zero of=/mnt/mem
bs=1024k count=512" if it changes the behavior. DAX forces synchronous
block allocations and unwritten-extent-zeroing that get skipped in the
page cache case.
> qemu-system-x86_64 -nodefconfig -nodefaults \
> -drive if=virtio,file=centos7.qcow2,index=0,media=disk \
> --enable-kvm -serial telnet:localhost:4443,server,nowait \
> -device sga -m 512 -smp 1,sockets=1,cores=1,threads=1 \
> -object memory-backend-file,prealloc=yes,mem-path=/mnt/mem,share=on,size=512M,id=ram
> \
> -numa node,nodeid=0,cpus=0,memdev=ram \
> -net nic,model=virtio,vlan=0 \
> -net user,vlan=0,hostname=vm,hostfwd=tcp:127.0.0.1:8001-:22 \
> -name test -monitor telnet:localhost:4444,server,nowait
>
> I use a headless host so I usually connect to the VM with 'telnet
> localhost 4443'.
>
> The above works and the VM boots in seconds.
> When adding '-o dax' to the mount command, I can catch the grub menu
> during boot but it gets stuck.
> Sometimes if I wait about 20 minutes, I see some kernel boot messages
> appear, but no errors.
>
> Any thoughts?
>
> Regards,
> Yigal
>
> [1] https://lwn.net/Articles/644675/
> _______________________________________________
> Linux-nvdimm mailing list
> Linux-nvdimm@lists.01.org
> https://lists.01.org/mailman/listinfo/linux-nvdimm
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next prev parent reply other threads:[~2017-04-20 13:23 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-20 9:19 qemu-kvm hangs with DAX Yigal Korman
2017-04-20 13:23 ` Dan Williams [this message]
2017-04-23 14:20 ` Yigal Korman
2017-04-24 6:16 Yigal Korman
2017-04-26 13:43 ` Paolo Bonzini
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