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Re: [Qemu-devel] [Bug?]When close VM the hugepage not freed
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [Bug?]When close VM the hugepage not freed |
Date: |
Tue, 14 Oct 2014 19:28:39 +0300 |
On Tue, Oct 14, 2014 at 01:08:15PM +0100, Daniel P. Berrange wrote:
> On Tue, Oct 14, 2014 at 08:02:38PM +0800, Linhaifeng wrote:
> > Hi,all
> >
> > I was trying to use hugepage with VM and found that the hugepage not freed
> > when close VM.
> >
> >
> > 1.Before start VM the /proc/meminfo is:
> > AnonHugePages: 124928 kB
> > HugePages_Total: 4096
> > HugePages_Free: 3072
> > HugePages_Rsvd: 0
> > HugePages_Surp: 0
> > Hugepagesize: 2048 kB
> >
> > 2.Start VM the /proc/meminfo is:
> > AnonHugePages: 139264 kB
> > HugePages_Total: 4096
> > HugePages_Free: 2048
> > HugePages_Rsvd: 0
> > HugePages_Surp: 0
> > Hugepagesize: 2048 kB
> >
> > 3.Close VM the /proc/meminfo is:
> > AnonHugePages: 124928 kB
> > HugePages_Total: 4096
> > HugePages_Free: 2048
> > HugePages_Rsvd: 0
> > HugePages_Surp: 0
> > Hugepagesize: 2048 kB
> >
> > We can see there are 1024 hugepage leak!
> >
> > I try to found which function used to free hugepage but i'm not sure
> > where the qemu_ram_free is the function to free hugepage.
> > I found that the qemu_ram_free function not call unlink and we know
> > unlink is used to free hugepage(see example of hugepage-mmap.c in
> > kernel source).
>
> We can't rely on 'qemu_ram_free' ever executing because we must
> ensure hugepages are freed upon QEMU crash.
>
> It seems we should rely on UNIX filesytstem semantics and simply
> unlink the memory segment the moment we create it & open the FD.
> That way the kernel will automatically free it when the FD is
> closed when QEMU process exits.
>
>
> Regards,
> Daniel
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