On 2014/10/17 21:26, Daniel P. Berrange wrote: > On Fri, Oct 17, 2014 at 04:57:27PM +0800, Linhaifeng wrote: >> >> >> On 2014/10/17 16:33, Daniel P. Berrange wrote: >>> On Fri, Oct 17, 2014 at 04:27:17PM +0800, haifeng....@huawei.com wrote: >>>> From: linhaifeng <haifeng....@huawei.com> >>>> >>>> The VM start with share hugepage should close the hugefile fd >>>> when exit.Because the hugepage fd may be send to other process >>>> e.g vhost-user If qemu not close the fd the other process can >>>> not free the hugepage otherwise exit process,this is ugly,so >>>> qemu should close all shared fd when exit. >>>> >>>> Signed-off-by: linhaifeng <haifeng....@huawei.com> >>> >>> Err, all file descriptors are closed automatically when a process >>> exits. So manually calling close(fd) before exit can't have any >>> functional effect on a resource leak. >>> >>> If QEMU has sent the FD to another process, that process has a >>> completely separate copy of the FD. Closing the FD in QEMU will >>> not close the FD in the other process. You need the other process >>> to exit for the copy to be closed. >>> >>> Regards, >>> Daniel >>> >> Hi,daniel >> >> QEMU send the fd by unix domain socket.unix domain socket just install the >> fd to >> other process and inc the f_count,if qemu not close the fd the f_count is >> not dec. >> Then the other process even close the fd the hugepage would not freed whise >> the other process exit. > > The kernel always closes all FDs when a process exits. So if this FD is > not being correctly closed then it is a kernel bug. There should never > be any reason for an application to do close(fd) before exiting. > > Regards, > Daniel > Hi,daniel
I don't think this is kernel's bug.May be this a problem about usage. If you open a file you should close it too. This is <<linux man page>>about how to free resource of file. http://linux.die.net/man/2/close I'm trying to describe my problem. For example, there are 2 VMs run with hugepage and the hugepage only for QEMU to use. Before run VM the meminfo is : HugePages_Total: 4096 HugePages_Free: 4096 HugePages_Rsvd: 0 HugePages_Surp: 0 Hugepagesize: 2048 kB Run the two VMs.QEMU deal with hugepage as follow steps: 1.open 2.unlink 3.mmap 4.use memory of hugepage.After this step the meminfo is : HugePages_Total: 4096 HugePages_Free: 0 HugePages_Rsvd: 0 HugePages_Surp: 0 Hugepagesize: 2048 kB 5.shutdown VM with signal 15 without close(fd).After this step the meminfo is : HugePages_Total: 4096 HugePages_Free: 4096 HugePages_Rsvd: 0 HugePages_Surp: 0 Hugepagesize: 2048 kB Yes,it works well,like you said the kernel recycle all resources. For another example,there are 2 VMs run with hugepage and share the hugepage with vapp(a vhost-user application). Before run VM the meminfo is : HugePages_Total: 4096 HugePages_Free: 4096 HugePages_Rsvd: 0 HugePages_Surp: 0 Hugepagesize: 2048 kB Run the first VM.QEMU deal with hugepage as follow steps: 1.open 2.unlink 3.mmap 4.use memory of hugepage and send the fd to vapp with unix domain socket.After this step the meminfo is: HugePages_Total: 4096 HugePages_Free: 2048 HugePages_Rsvd: 0 HugePages_Surp: 0 Hugepagesize: 2048 kB Run the second VM.After this step the meminfo is: HugePages_Total: 4096 HugePages_Free: 0 HugePages_Rsvd: 0 HugePages_Surp: 0 Hugepagesize: 2048 kB Then I want to close the first VM and run another VM.After close the first VM and close the fd in vapp the meminfo is : HugePages_Total: 4096 HugePages_Free: 0 HugePages_Rsvd: 0 HugePages_Surp: 0 Hugepagesize: 2048 kB So failed to run the third VM because the first VM have not free the hugepage.After apply this patch the meminfo is: HugePages_Total: 4096 HugePages_Free: 2048 HugePages_Rsvd: 0 HugePages_Surp: 0 Hugepagesize: 2048 kB So i can run the third VM success. -- Regards, Haifeng
