From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:57232) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XeIci-0004MW-IS for qemu-devel@nongnu.org; Wed, 15 Oct 2014 03:03:56 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XeIce-000569-Qc for qemu-devel@nongnu.org; Wed, 15 Oct 2014 03:03:52 -0400 Received: from mx1.redhat.com ([209.132.183.28]:10383) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XeIce-000561-IY for qemu-devel@nongnu.org; Wed, 15 Oct 2014 03:03:48 -0400 Date: Wed, 15 Oct 2014 08:03:34 +0100 From: "Daniel P. Berrange" Message-ID: <20141015070334.GB11721@redhat.com> References: <543D10DE.2080109@huawei.com> <20141014120815.GA29671@redhat.com> <20141014162839.GA17071@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20141014162839.GA17071@redhat.com> Subject: Re: [Qemu-devel] [Bug?]When close VM the hugepage not freed Reply-To: "Daniel P. Berrange" List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: lilijun , Linhaifeng , qemu-devel@nongnu.org On Tue, Oct 14, 2014 at 07:28:39PM +0300, Michael S. Tsirkin wrote: > 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. > > > We being libvirt? No, QEMU is responsible for creating the mmap file, so QEMU should take care of unlinking it after opening it. Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :|