On Fri, Jul 13, 2012 at 02:08:06PM -0700, Andrew Morton wrote: > On Fri, 13 Jul 2012 14:48:08 +0300 > "Kirill A. Shutemov" <kirill.shute...@linux.intel.com> wrote: > > > From: "Kirill A. Shutemov" <kirill.shute...@linux.intel.com> > > > > free_nsproxy() is too heavy to be on exit path. Let's free namespaces > > asynchronously to not block exit_group() syscall. > > Please be specific, and complete. > > Why is it "too heavy"? Where is the time being spent? Is it spent in > D state or is it spent burning CPU cycles? Does the patch simply > offload the work into kernel threads, providing no net gain?
Unpatched switch_task_namespaces() takes 0.010 - 0.011 seconds on my machine. About 0.008 of the time is synchronize_rcu(). So it's mostly waiting with wait_for_completion() in wait_rcu_gp(). It means D state. > > The patch also fixes bug with free namespace without synchronize_rcu() > > through > > put_nsproxy(). > > I just don't understand this description. IIUC current locking model requires synchronize_rcu() before free_nsproxy(). put_nsproxy() calls free_nsproxy() without synchronize_rcu(). So it's racy. I guess it was missed during switch to RCU (see cf7b708). Pavel, am I right? > Please send a new one which > includes all details about the bug, including a description of > the user-visible effects of the bug. Okay, I will. -- Kirill A. Shutemov -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
