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Date: Tue, 14 Oct 2014 19:28:39 +0300
From: "Michael S. Tsirkin" <mst@redhat.com>
Message-ID: <20141014162839.GA17071@redhat.com>
References: <543D10DE.2080109@huawei.com> <20141014120815.GA29671@redhat.com>
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Subject: Re: [Qemu-devel] [Bug?]When close VM the hugepage not freed
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To: "Daniel P. Berrange" <berrange@redhat.com>
Cc: lilijun <jerry.lilijun@huawei.com>, Linhaifeng <haifeng.lin@huawei.com>, qemu-devel@nongnu.org

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

We being libvirt?

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