Re: [Qemu-devel] [PATCH] fix the memory leak for share hugepage

[Daniel P. Berrange]

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, address@hidden wrote:
> >> From: linhaifeng <address@hidden>
> >>
> >> 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 <address@hidden>
> > 
> > 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
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